Adult Discus: How Much Water Exchange Is Enough?

[afriend]

Hi All,

I'm the one who started the thread "Water Changes" a few weeks ago. When I left my last input, I stated that I was going to get a TDS meter, make some tests, and get back and report the results. At that time I was somewhat pessimistic about being successful at my endevor, but I told you that I would report my results one way or the other.

This is only an interim report as to what I have achieved since then. I now have a TDS meter and have acquired and recorded data in my Engineering Laboratory Notebook (using the same general process that I did before retirement as an Aeronautical Engineer working in research and development), and I now have a little more experience in a new field that I knew almost nothing about a few weeks ago. This has brought me to a point where I see the picture a little better (at least I hope so) and as a result have redifined my objective somewhat.

First of all, let me set up a little background information as to what my objective is now about. I start with the belief that water quality is a key element in successfully keeping ADULT discus. (My endeavor is constrained to adult discus only and also to tanks without plants.) I have made the following assumptions: water entering the discus tank has parameters favorable to the fish (good quality by definition), fish food is the major source of contamination (fish eat part of it and the remainder rots), and lastly water and filter exchange is the major way that the contamination is removed from the tank (siphoning stuff off the tank bottom is part of this exchange process.) I am attempting to answer two questions: can a TDS meter be used to measure the contamination accumulating in the tank, and second, how much water exchange is necessary to keep the contaminations within acceptable limits. Ultimately I would like to get to the position where I could recommend that sufficient water exchanges be made to keep TDS contaminations below XXX ppm.

I have been recording daily results of my testing in my ELN and now have sufficient data to substantiate the following observation: a TDS meter can be used to measure the effect of accumulating contamination due to fish food. Also, I can probably provide a quantative measure of how much TDS builds up on a per fish per day basis. I'm not finished with this yet, so I do not want to provide details until I'm sure of my results. This takes time, so it may be a few more weeks before I'm ready to state my results. Be assured that I will do this and report both favorable and not so favorable results. But the good news so far is that I'm pretty sure that I have a worthwhile experiment going since I have a repeatable method of measureing contaminates.

Please provide suggestions, comments, ideas, questions, or anything else (within reason) that may assist me. I really appreciate input from each and every one at this forum, especially those of you with lots of experience with discus.

[shoveltrash]

I read that "a TDS meter measures the conductivity of the solution and estimates the TDS from that." - is bio-contamination (feces/food) conductive?
I'm also of the opinion that clean water (free of bio-contaminants) is key.



I now have a little more experience in a new field that I knew almost nothing about a few weeks ago. This has brought me to a point where I see the picture a little better (at least I hope so) and as a result have redifined my objective somewhat. funny, I'm having a similar experience......I now know more about water parameters than I ever dreamed! I started talking GH/KH, pH, etc at work yesterday and got some funny looks LOL!!! (btw I work in Surgery/Operating Room nurse :) )

good luck with this Paul -- your thorough systematic approach really appeals to me. looking forward to reading more!

[pcsb23]

TDS meters measure conductivity and then "guess" at the TDS. Only way to truly get to the TDS is via titration. Be careful of falling into the "Analysis to Paralysis" trap, we are dealing with living organisms not an engineering problem :)

You should also be logging pH as this has a dramatic effect on conductivity. A very simple experiment is to get a couple of pints ( or 1 litre) RO water (or DI water) and measure the TDS, then add 1 drop of HCL to it and measure again. Add another drop and measure once more, what you will see is a dramatic rise in TDS yet were this titrated the actual TDS would be very little. The reason for this is that HCL causes more H+ ions to be available hence increasing the conductivity of the water.

As the biofilter works it breaks down ammonia into nitrite, and then into nitrates. One of the by products from this process is nitric acid, this is one of the very strongest acids out there so readily lowers the pH of the aquarium. A lower pH means more H+ ions which means you will get a higher reading on the TDS meter (which uses conductivity as it's method of measure).

[afriend]

I read that "a TDS meter measures the conductivity of the solution and estimates the TDS from that." - is bio-contamination (feces/food) conductive?
I'm also of the opinion that clean water (free of bio-contaminants) is key.


funny, I'm having a similar experience......I now know more about water parameters than I ever dreamed! I started talking GH/KH, pH, etc at work yesterday and got some funny looks LOL!!! (btw I work in Surgery/Operating Room nurse :) )

good luck with this Paul -- your thorough systematic approach really appeals to me. looking forward to reading more!

Yes, my TDS meter estimates TDS by measuring conductance of the water. Does it measure actual TDS? I don't know. I have decided to refer to my measurements using a TDS meter as "TDS readings". What I do know is that for the purposes of my experiment, I can obtain repeatable (within 1ppm) measurements of my water source, the water in my aquarium, the water from my RO filter, and other water samples that I have performed experiments in. However, I have concluded that it is probably not suited for taking readings of water leaving my water softner.

Are feces/food conductive? Yes, at least part of it is. Undoubtably they both contain a mixture of organic and inorganic material, and I have no way of knowing how much of each. What I do know is that different foods produce a wide range of TDS readings when they are disolved in water. When working with a specific food, with the same mixture ratio of food and water, the TDS readings are repeatable (within reason).

I agree with the basic intent of your statement about the necessity for clean water. But the fish in our aquariums do not live in an environment free from bio-contaminates. So where does the compromise lie between how much water exchange is necessary to keep the conditions healthy for them? That's the question I'm trying to study. I have sufficient data recorded to date that indicates how TDS readings in my aquarium vary throughout a 24 hour period and from day to day. The TDS readings decrease (as predicted) when the water exchange occurs and increases throughout the day, especially when I feed them. Also, the TDS readings are repeatable generally within 1ppm. If you were to put me in a black box and give me only two TDS readings (water source and aquarium water) I could tell you the approximate time of day.

Thank you Trish for your kind response. It helps me to know that others are interested in my endevor. What I would like everyone to know is that I presently have no idea if I will be successful in my task. But it's fun to try, especially when some people try to indicate that it's impossible. I believe that the answer to my question is an important thing to know for the discus loving community. If I can shine a little light on the question, maybe I can contribute something.

Paul

[ericatdallas]

I am attempting to answer two questions: can a TDS meter be used to measure the contamination accumulating in the tank, and second, how much water exchange is necessary to keep the contaminations within acceptable limits. Ultimately I would like to get to the position where I could recommend that sufficient water exchanges be made to keep TDS contaminations below XXX ppm.



With the second question: and second, how much water exchange is necessary to keep the contaminations within acceptable limits.

Not all contaminations are created equal. Your TDS measurements may be recording 'contaminants' that are benign. Would ascorbic acid change TDS measurements? Studies show that higer concentration of ascorbic acid (vitamin C), improves the health of fish as compared to a control group and experimental groups with lower concentrations.

Also, the contamination of the water from other elements is going to be highly correlated with the nitrates in a BB tank. So if you target a low nitrate level (which studies have shown that nitrate level is important) then you're going to simultaneously get rid of any other contaminants. Which is why nitrates is the metric most aquarists go by.

[aalbina]

Paul,

As others have stated, I think that you need to factor in other variables that are present in the "system" and will have a significant impact on outcome of your study. pH is a major variable to consider since the instrument your using to measure TDS is effected by pH. It would be interesting to track the rise and fall of pH along with TDS to see if those to factors can be positively or negatively correlated. There are likely others that need to be considered especially if you intend to draw causation from your research in lieu of statistical significance.

Your research assumptions: "fish food is the major source of contamination (fish eat part of it and the remainder rots)" - might need some clarification. I think ammonia will be produced by fish even if they are not fed, it is part of the respiration process. I don't know how much ammonia would accumulate in the water if fish were not fed, but nitrite and finally nitrate would eventually be byproducts of the biological filtration of ammonia. That will effect TDS as well. Perhaps in an insignificant way - but I'm not sure.

I'm not sure that your hypothesis "a TDS meter [can] be used to measure the contamination accumulating in the tank" is measureable. The problem is the definition of contamination and it's subsequent correlation to water quality and then fish health. As an example, copper contamination in freshwater reaches LC50 (lethal concentration, mortality rate of 50%) between .02 and .05ppm depending on species. Water hardness reduces the toxicity of copper sometimes by 20 times or more. So the chemistry (pH, hardness, alkalinity) of the water has a huge impact on what one considers lethal or detrimental contamination. http://www.science.mcmaster.ca/Biology/4S03/COPPER.HTM Additionally, the measurement of TDS using your method is also effected by water chemistry - copper is highly conductive and will raise the TDS. It's not the raising of TDS that killed the fish - its the content of what raised the TDS. Salt also raises the TDS - but generally doesn't kill fish. So after you've compiled your data you may be tempted to draw conclusions based on the variables you have recorded when the truth may be revealed using a multivariant analysis of variables you have not recorded.

I think your work is interesting and I'm looking forward to your results - I would just caution that unless you are able to capture accurate, broad, multivariant data, your results will be less valuable to you and perhaps even lead you, and others, to conclusions that may not be entirely supportable.

Good luck!

Adam

[afriend]

TDS meters measure conductivity and then "guess" at the TDS. Only way to truly get to the TDS is via titration. Be careful of falling into the "Analysis to Paralysis" trap, we are dealing with living organisms not an engineering problem :)

You should also be logging pH as this has a dramatic effect on conductivity. A very simple experiment is to get a couple of pints ( or 1 litre) RO water (or DI water) and measure the TDS, then add 1 drop of HCL to it and measure again. Add another drop and measure once more, what you will see is a dramatic rise in TDS yet were this titrated the actual TDS would be very little. The reason for this is that HCL causes more H+ ions to be available hence increasing the conductivity of the water.

As the biofilter works it breaks down ammonia into nitrite, and then into nitrates. One of the by products from this process is nitric acid, this is one of the very strongest acids out there so readily lowers the pH of the aquarium. A lower pH means more H+ ions which means you will get a higher reading on the TDS meter (which uses conductivity as it's method of measure).

I'm aware of how a TDS meter based on conductivity arrives at a measurement. My approach does not depend on getting a true measure of TDS so long as the measurement is proportional to the "stuff" in the tank that is due to the portion of the food disolved in the water and the portion that the biological process of the fish produces.

Not quite sure what you mean by the statement "Analysis to Paralysis trap, we are dealing with living organisms not an engineering problem." 1) Could you please elaborate on what you mean by your referenced trap. 2) The following is an oversimplification of course, but it looks like an engineering problem to me "nice clean water going into the tank, food and fish poop cause contamination, water exchanges reduce contamination. What does one need to do to keep contaminates below an acceptable level?"

In regards to your suggestion about logging PH, I already record PH along with some other parameters. The variation of PH in my tank is much smaller than the variation of my PH meter (about 0.1). Also, I performed the simple experiment you mentiond with RO water some time ago when I first set up my discus tank. I measured PH as a function of the fraction of well water added to RO, thats how I arrived at the 20% figure.

As far as nitrates are concerned, my water exchanges are somewhat more than is necessary to maintain a nitrate level near zero. If I maintain water exhanges sufficient to keep nitrate levels near zero, do you know if TDS measurements will be affected by the nitric acid produced as a by product of the ammonia/nitrite/nitrate cycle?

Thank you for your very kind response

[ericatdallas]

If you're doing enough water changes to keep nitrates near zero, wouldn't that keep your 'contaminant' levels near the levels of tap water?

[afriend]

[QUOTE=aalbina;835824]Paul,

As others have stated, I think that you need to factor in other variables that are present in the "system" and will have a significant impact on outcome of your study. pH is a major variable to consider since the instrument your using to measure TDS is effected by pH. It would be interesting to track the rise and fall of pH along with TDS to see if those to factors can be positively or negatively correlated. There are likely others that need to be considered especially if you intend to draw causation from your research in lieu of statistical significance.

Your research assumptions: "fish food is the major source of contamination (fish eat part of it and the remainder rots)" - might need some clarification. I think ammonia will be produced by fish even if they are not fed, it is part of the respiration process. I don't know how much ammonia would accumulate in the water if fish were not fed, but nitrite and finally nitrate would eventually be byproducts of the biological filtration of ammonia. That will effect TDS as well. Perhaps in an insignificant way - but I'm not sure.

I'm not sure that your hypothesis "a TDS meter [can] be used to measure the contamination accumulating in the tank" is measureable. The problem is the definition of contamination and it's subsequent correlation to water quality and then fish health. As an example, copper contamination in freshwater reaches LC50 (lethal concentration, mortality rate of 50%) between .02 and .05ppm depending on species. Water hardness reduces the toxicity of copper sometimes by 20 times or more. So the chemistry (pH, hardness, alkalinity) of the water has a huge impact on what one considers lethal or detrimental contamination. http://www.science.mcmaster.ca/Biology/4S03/COPPER.HTM Additionally, the measurement of TDS using your method is also effected by water chemistry - copper is highly conductive and will raise the TDS. It's not the raising of TDS that killed the fish - its the content of what raised the TDS. Salt also raises the TDS - but generally doesn't kill fish. So after you've compiled your data you may be tempted to draw conclusions based on the variables you have recorded when the truth may be revealed using a multivariant analysis of variables you have not recorded.

I think your work is interesting and I'm looking forward to your results - I would just caution that unless you are able to capture accurate, broad, multivariant data, your results will be less valuable to you and perhaps even lead you, and others, to conclusions that may not be entirely supportable.


Adam,

I took me a little while to figure out what you were trying to tell me. Let me explain it this way. There are all sorts of contaminants. What I'm calling contaminates here are those that build up in the tank due to feeding the fish. There are of course many other types of contaminates (copper for one). Lets say for the sake of discussion that your water supply contained disolved copper at the concentration of 1ppm. Let us assume that you filled your tank with this water, and then later made a water exchange . Let us assume that evaporation is not an issue. Copper will not accumulate in your tank, it will always be 1ppm. This is true of all other elements entering the tank thru water exchanges. So in my study I am not considering anything entering the tank thru water exchange as a contaminant.

I have a very stable water source. I use a 20% mixture of well water mixed with RO water. The PH and the measured TDS of this source water is extremely stable. What I have determined is that the measured TDS of water in my tank varies hour by hour, depending on when I feed the fish and when the water changes occur. The lowest amount of measured TDS is right after a water exchange. It then increases thru the day and night until the next water exchange. Furthermore I know that that the amount of this TDS variation is in proportion to the number of fish in the tank. Beyond that, I'm still experimenting to get more data under different circumstances. Please note that what I am calling contamination is that portion of measured TDS that varies

One other thing that I know is that the increase in measured TDS during the cycle period is not due to accumulating nitrates. My water exchange rate is sufficent to maintain the level of nitrates near zero.

Yes, I aware that there are a number of other variables that must be considered. I'm hoping that members of this forum will point these out, just so I don't screw this up.

Thanks for your thoughfull input.

Paul

[afriend]

If you're doing enough water changes to keep nitrates near zero, wouldn't that keep your 'contaminant' levels near the levels of tap water?

Eric,

Good question. The answer is that what I'm calling contaminates (the part of the TDS measurement that varies) is somewhere between 10 and 100 times greater than nitrate.

My water supply contains 0ppm nitrates, so the only nitrates have to deal with is that due to the biological cycle.

Thanks Eric.

Paul

[pcsb23]

Analysis to Paralysis is a phrase often used in sports coaching, it means over thinking things to the point where you miss the obvious or become incapable of making a decision.

Your over simplification is in fact a nice model imo, and inevitably there will be variables. Using a TDS meter as a guide is a sensible approach.

One of the things I always try to do is to find the simplest solution to any problem, and if I can find a simple solution that also has in a large margin of tolerance then so much the better. In my case rather than use an arbitrary reading, albeit one arrived at by research, I would do higher water changes and at a higher frequency than suggested by the research. The main reasons for this is that it is simple and proven.

What would be a really interesting experiment would be to collect your data over the lifetime of a group of discus, whilst running another group under the more common method of BB and regular large water changes. May be one for when I am retired, sadly that day is too far away :(

[afriend]

Hi All,

I want to quote something from a report I ran across while researching my little experiment. Its a really well written report by Niels Jensen titled "The Importance of Total Dissolved Solids in the Freshwater Aquarium". I don't know when it was written, but it was posted on Plecoplanet about December 2009. There's a lot of stuff in it about water chemistry as it concerns the freshwater aquarium. I was particularly interested in the part of the report that states:

"I now regard TDS levels as a means of deciding on when to do a water change. A rise in TDS levels means I need to change some water and thereby lower TDS levels. Rapidly increasing TDS levels can also indicate over-feeding, an over-stocked tank, or general bad maintenance."

So I am by no means the first to consider the relationship between TDS levels and water changes.

Neils Jansen does not provide any other information in the report about TDS levels and water changes, so this is where I thought I could perhaps take this one step further. If I am successful at my endevor, I will be able to provide a mathematical equation relating TDS level with tank size, frequency and amount of water change, number of adult discus, and some sort of measure of feeding. This won't result in a precise determination of course, but rather a rough measure of what is happening in our aquarium water. Perhaps my work will encourage someone else to improve on what I accomplish. (If I accomplish anything at all, because I may go down in a glory of smoke and flame).

Paul

[afriend]

Analysis to Paralysis is a phrase often used in sports coaching, it means over thinking things to the point where you miss the obvious or become incapable of making a decision.

Your over simplification is in fact a nice model imo, and inevitably there will be variables. Using a TDS meter as a guide is a sensible approach.

One of the things I always try to do is to find the simplest solution to any problem, and if I can find a simple solution that also has in a large margin of tolerance then so much the better. In my case rather than use an arbitrary reading, albeit one arrived at by research, I would do higher water changes and at a higher frequency than suggested by the research. The main reasons for this is that it is simple and proven.

What would be a really interesting experiment would be to collect your data over the lifetime of a group of discus, whilst running another group under the more common method of BB and regular large water changes. May be one for when I am retired, sadly that day is too far away :(

Paul,

I really like your sports coaching phrase. Sure hope I'm not over thinking this and overlooking the obvious. That's why I like to have comments from others, makes me think about it more (HA).

Hope you don't think I was being flippant with my oversmplified statement about this being an engineering problem. The basic truth here is this: "So what if I develope an equation relating TDS to tank size, frequency and amount of water changes, number of adult discus, and a measure of feeding, how am I going to determine how much TDS is too much?" Right now, I really don't know how to do that.

Back when I posted the first thread on this subject, I asked the question "how much water exchange is enough?" I was surprised in the broad range of water exchanges that respondents came up with. It seemed that there was little to no agreement amoung them. But this is also true of a number of issues similar to it. While I agree with you that one should provide more exchange than necessary, in my case I had no idea where to begin at, so I immediately increased my water exchange rate to 50% daily. So I did exactly as you did.

I am retired and have been for 17 years now. I really miss the challenge of research work. So that's my real motivation in this endeavor. But I got to tell you that water chemestry is not my bag at all. (I really didn't care much for chemistry when I was in engineering school.) However I do enjoy learning something new. What do you do for a living?

Thanks for your very thoughtful reply. Please feel free to point me in the right direction.

Paul

[ShinShin]

K.I.S.S.

Long before we had all this fancy equipment, discus were being kept and bred by experienced fish people. Their years of dedication to the hobby gave us guidelines for successful discus keeping. 1 adult for 10 gal of water with a minimum of 10% daily water change was found to be the minimum parameters. More water, better results.

[pcsb23]

Paul,

I really like your sports coaching phrase. Sure hope I'm not over thinking this and overlooking the obvious. That's why I like to have comments from others, makes me think about it more (HA).

Hope you don't think I was being flippant with my oversmplified statement about this being an engineering problem. The basic truth here is this: "So what if I develope an equation relating TDS to tank size, frequency and amount of water changes, number of adult discus, and a measure of feeding, how am I going to determine how much TDS is too much?" Right now, I really don't know how to do that.No I didn't feel you were being flippant :)



Back when I posted the first thread on this subject, I asked the question "how much water exchange is enough?" I was surprised in the broad range of water exchanges that respondents came up with. It seemed that there was little to no agreement amoung them. But this is also true of a number of issues similar to it. While I agree with you that one should provide more exchange than necessary, in my case I had no idea where to begin at, so I immediately increased my water exchange rate to 50% daily. So I did exactly as you did.Shows there is more than one way, and no such thing as only one right way :)



I am retired and have been for 17 years now. I really miss the challenge of research work. So that's my real motivation in this endeavor. But I got to tell you that water chemestry is not my bag at all. (I really didn't care much for chemistry when I was in engineering school.) However I do enjoy learning something new. Having something to get engrossed in is good, and I too enjoy learning. A friend of mine on another discus forum has the following tag line "Patience , Routine , Enjoyment , Reward." He's right too imo.


What do you do for a living?I am back working as a software engineer :(



Thanks for your very thoughtful reply. Please feel free to point me in the right direction.

PaulI agree with Mat (ShinShin) keep it simple, however using technology to help us make informed decisions is no bad thing, provided we don't totally rely on it.

[afriend]

K.I.S.S.

Long before we had all this fancy equipment, discus were being kept and bred by experienced fish people. Their years of dedication to the hobby gave us guidelines for successful discus keeping. 1 adult for 10 gal of water with a minimum of 10% daily water change was found to be the minimum parameters. More water, better results.

Dylan,

KISS: Yea, I agree I'm somewhat stupid sometimes, but I do like to keep it simple if I can.

Humor aside, I would appreciate it if you could provide a source for your "1 adult for 10 gal of water with a minimun 10% daily change." Is this something you obtained thru talking with others, based on your own experience, or is there a written source that I could look up? If I can substantiate this, it could be a valuable data point for my study. There seems to be a reasonable amount of agreement on the 10 gal/ adult discus portion, but none of the 1200 respondents on my prior thread about water changes came up with the 10% figure. In fact, after spending a few hours using the Simply Discus search feature, I could not find any post that mentions 10% daily change as a minimum. Perhaps I overlooked something, could you please point me in the right direction?

I learned a few things while using the Simply Discus search feature. First, the question as to how much water exchange is necessary is a hotly debated subject. If I were to summarize, I would say that there is no general agreement on how much water to exchange, and that the recommendated range varies greatly. So it probably looks to me now that I won't be able to settle any differences of opinion on how much water exchange is necessary. However, I do think that I have something to contribute providing that my study is successful. If I can come up with a mathematical equation that relates TDS measurements to tank size, frequency and amount of water changes, number of adult discus, and some measure of feeding, perhaps this will help put a little more light on the subject.

Concerning your statement "more water, better results". Surely there has to be a point of diminishing returns.

Help and guidance from you and others would be greatly appreciated.

Thanks very much for your input. I'm looking forward to your addressing the questions herein and reply.

Paul

[ShinShin]

Paul,

That was just a figure that was used for years on various forums and publications. Personally, for adults and breeding pairs, I subscribe to Wattley's 40% daily water changes. Juvies growing out, 80-90%. Jack used that figure in a talk I attended on Long Island in the mid 90's and I most likely saw it in his column in TFH.

Mat

To clarify, 40% was Jack's. The 80-90% for juvies was what I do.

[nc0gnet0]

Not all contaminates effect the TDS reading on your meter. As was mentioned, in order to do so, the contaminate would have to effect the conductivity of the water. The TDS meter is a great tool for measuring conductive elements like calcium and magnesium, not so great for measuring dissolved organics like fish poo and urea. Try adding a capfull of meth blue to a 20 gallon tank and take a measurement both before and after. You will find TDS is completely uneffected, yet it is obvious there is a contaminate in the tank that wasn't there previously.

So while the concept of what you are trying to do looks good on paper, the limitations on the tools you are using to conduct your "research" will render your results almost meaningless.

Not sure exactly how much water you are exchanging each day now, but as the total amount of water you change each day goes down, the larger the effect TDS creep will skew your findings unless you have a method of accounting for evaporation.

Think less along the lines of an enginering research and more along the lines of medical research. There is a way to do this, but it's going to take a lot more fish tanks ;)

Rick

Rick

[afriend]

Not all contaminates effect the TDS reading on your meter. As was mentioned, in order to do so, the contaminate would have to effect the conductivity of the water. The TDS meter is a great tool for measuring conductive elements like calcium and magnesium, not so great for measuring dissolved organics like fish poo and urea. Try adding a capfull of meth blue to a 20 gallon tank and take a measurement both before and after. You will find TDS is completely uneffected, yet it is obvious there is a contaminate in the tank that wasn't there previously

Yes, I understand what you have said here and agree completely. I have done enough reading to get an idea of what can and cannot be measured with a TDS meter, and have determined that there is a limitation on what types of organic compounds are detected. So what I am now doing is to disolve various types of fish food and fish feces in a separate tank to determine their conductivity. I am reasonably confident to be able to say that all the foods tested to date are conductive to a degree and that the amount of conductivity is proportional to the quantity disolved.


So while the concept of what you are trying to do looks good on paper, the limitations on the tools you are using to conduct your "research" will render your results almost meaningless.

That may well be the case. If it turns out that way, I'll be the first in line to admit failure. In the meantime I hope that you don't mind too much if I try. By the way, I have not refered to my little project as "research". Most of my engineering career was involved with research, and I know that I'm not prepared or equipped to do research in this field. Thats why I have refered to this in this thread as an experiment.


Not sure exactly how much water you are exchanging each day now, but as the total amount of water you change each day goes down, the larger the effect TDS creep will skew your findings unless you have a method of accounting for evaporation.


The range of water exchange I'm working with is 10 to 50% daily. I'm aware that there will be an increase concentration of conductive material due to evaporation. My aquarium has a top which limits evaporation and I am confident that the exchange rate is considerably greater than the evaporation. If this were not the case I could take this into consideration by calculating the increase concentration by measuring the amount evaporated.


Think less along the lines of an enginering research and more along the lines of medical research. There is a way to do this, but it's going to take a lot more fish tanks

I understand your statement here. However, will all due respect, you don't fully understand what I'm attempting to accomplish. Would suggest that you re-read the thread from the beginning. Would be glad to explain it in greater detail after you have done so.

Thank you very much for your input.

Paul

[judy]

I will continue to follow your progress with great interest, Paul. If only because I would like to be able to make deductive use of the costly TDS meter i purchased ages ago-- and never use!

[afriend]

Judy, hope I don't disappoint you. But then maybe you can find another use for it, like a paper-weight or convert it to a tire pressure gauge.

Paul

[afriend]

Rick,

Since the time I replied to your response above, I have given a lot of thought about a couple of issues you brought up and I now see some things quite a bit different.


Not sure exactly how much water you are exchanging each day now, but as the total amount of water you change each day goes down, the larger the effect TDS creep will skew your findings unless you have a method of accounting for evaporation.


Yea, your right. When I had initally thought about evaporation, I dismissed it because I considered it to be a small effect. However, on second thought I decided to do some calculations and then determined that evaporation in this case can cause TDS creep and thereby skew the results (just like you stated). This inclines me to think that you may know more about this process than myself. Please understand that water chemistry is nothing at all like my field of expertise (spacecraft navigation, guidance and control). The two fields have almost nothing in common, so I am really a novice in the field of water chemistry. Glad to have you pointing me in the right direction. By the way, how did you come by the knowledge of TDS creep?



Think less along the lines of an enginering research and more along the lines of medical research. There is a way to do this, but it's going to take a lot more fish tanks

I understand this too. And the further I get into my little experiment, the more I appreciate exactly what your statement here is telling me. I don't have the equipment or the money to perform this sort of thing, but someone could do the discus loving community a big favor by accomplishing exactly that. Water exchange is a very important issue, and there is a very wide range of opinions (among the best people who work with discus a lot) as to how much water to exchange. If someone was willing to come up with a few thousand dollars, I'd love to devote the time to accomplish it.

Thank you so very much for your thoughtful submission. Of those who have responded, yours has helped me the most. Please forgive me for initally dismissing your ideas before thinking it thru.

Paul