Changing water -- fish-days/gallon

[Anonapersona]

I've been thinking about how one knows how many fish to stock and how much water to change and how often. After hanging around here for while, I've started to develop a feel for what the group might suggest, and as my own fish have grown I can see how stocking density looks in the tank in terms of agression and waste. But, the engineer in me needs to quantify what I see.

I know that the water change volume used yields a limit to the accumulation of waste in the tank, and that limit is the inverse of the water change fraction. So a 30% water change eventually leaves 1/0.30 days of waste in the tank or 3.3 days waste is the upper limit (lets just assume that there are wastes produced by fish that remain in adequately filtered water.)

If you multiply that DaysWaste value by the number of fish in the tank and divide by the nominal tank size you get a fish-day/gallon value. This value is not adjusted for fish size.

So, 9 fish in 55 gallons getting 50% a day is 9 Fish x (1day/0.50change)Days / 55 gallons = 0.33 Fish-Days/Gal

And 12 fish in 20 gallons getting 50% twice a day is 12 Fish x (0.5day/0.50change)Days /20 gallons = 0.60 Fish-Days/Gal

I looked back at stocking and water change numbers that people have offered here in SimplyDiscus to see if there was a trend. The fish-day/gal number varied between posters from 0.60 to 0.30 as the normal range with max of 1.5 and a min of 0.15.

So, I am hoping that this ratio might help people to understand why Carol might advise someone to do 50% water changes on 9 juveniles in a 55 gallon tank and then do 30% water changes on 5 adults in a 55 gallon tank -- as that keeps the ratio at 0.3 which is pretty darn good. And Burnaby's 4 discus in 240 gallons with 20%WC/wk are just as happy as Harriet's 9 fish in 180 gallons with 60%WD/wk as each ratio is 0.58, which each seemed to think was near an upper limit for planted tanks.

From searching old posts here, Carol typically suggests a ratio of 0.3, Lester keeps a ratio of 0.3, Shive has ratios reported of 0.15, 0.3, and 0.6 on various tanks, Phil Edwards advised Wildy to lower his ratio to 0.6, Tri reported 0.2, April has 0.4, Willie has 0.7 with his 10 gallons per fish and 100% WC per week.

DaveC reported 1.5 with 3" fish and it is outside of the normal ratios I saw, that was 50 3" fish in 65 gallons with 50% WC per day -- if that is correct I suspect the water must be perfect and rather acid to make it work, or maybe he siphons it during the day, but I'm just guessing.

With frequent siphoning of the bottom perhaps that is so, for that 1.5 is the ratio I was running on the baby tank with 23 fish and 25%WC in 60 gallons and I clean the bottom 2 to 3 times a day. But recently they began to get a bit more agressive and so while it doesn't look too crowded in there, I realized that the days of fish waste was getting too high. So, I have increased this to 60%WC to get to a ratio of 0.6 but I can see that I have to get rid of fish soon.

Maybe this will help someone understand how fish density relates to required water changes. Yes, it does not allow for the difference between small fish and large fish, or acid water vs alkaline water, or types of filtration. But, run the numbers on your tanks, and tell me if it seems reasonable. I am interested to see if there is a ratio that turns up to be appropriate for babies vs juveniles vs adults vs planted tanks. And whether acid vs alkaline water or hard water vs soft water makes a difference.

[GulfCoastDiscus]

Boy Ann, you make something easy complicated. :)

To me it's all by feel and observation. Your fish will tell you if they are healthy or need more w/c. I don't think it can be put into a formula. People have different water and there's that untestable parameters in the water column. What works for others might not work for you and vice versa. JMO

Dan

[Carol_Roberts]

That's pretty interesting. I've always wondered if You could get by with less water changes in softer or more acidic water than my GH 12, pH.7.8 water. April's water is very soft and prone to pH crash, yet her ratio is similiar to mine. (0.3 vs. 0.4)

I think the folks with plants are factoring the needs of the plants with the needs of the discus and so have higher numbers (which are less than optimum for discus, but better for plants)

[Anonapersona]

Carol, your suggestions were the most interesting, as they were so consistent!

In a post of 9/16/03 you suggested to someone that
2 fish in a 29 should have 30%WC/day (ratio = 0.23)
9 juveniles in a 55 should have 50%WC/day (ratio = 0.33)
5 adults in a 55 should have 30%WC/day (ratio = 0.30)

then 4/22/03 you said
12 juveniles in a 55 should have 80%WC/day (ratio = 0.27)

It seems that you have enough experience to juggle these numbers unconciously in your head -- that's why I'm trying to quantify it, you are clearly basing this on your experiences.


Dan, I am really just trying to take the magic out of it.

I've seen so many posts from people who show up and ask how many fish can they keep in this tank but they don't want to do many water changes, and they get an answer but they have a hard time understanding why that is the answer.

By directing a novice to start at a good point and then giving them some tools to use to see when things are changing, they will develop the "feel and observation" hopefully before they kill any fish.

Like the fellow who posted from Saudi (?) who was doing 10% WC weekly, every 3 months his fish got sick, he treated with meds, did a huge water change and they got better. After a new tank of water it took a while for the waste to build up to the 10 weeks of waste times how ever many fish he had and so after so many weeks they started to feel bad again until they actually got sick. That post was one that got me to thinking about this. Not to pick on him, for there are so many others that I see both here and over at other forums, but that one was dramatic for I saw that the water change was what was perking up the fish, more than the meds he used.

So, I think if we can give them a reason, and a way to monitor that, "the best fish keepers shoot for a ratio of 0.3 to perhaps 0.6, 0.6 particularly for planted tanks. And we also see that if you keep it siphoned several times a day that ratio may go to 1.5 for very small fish, and 0.6 for juveniles, as long as you are keeping the tank very clean."

You can have more fish if you'll change more water, or less fish if you change less water -- and this is how those things are related. Not to dictate to someone what to do, but allow them to see how the choices are layed out, where the danger zones are.

Anona, with a fish waste ratio of 0.76 with twenty three 3-4" juveniles in a 60 gallon tank, now getting 50%WC daily, siphoned clean twice a day.

[Dkarc@Aol.com]

IMO, the amount of w/c's needed depends upon 2 things, the pH and the biological capacity of your filter(s). Now, one thing you need to understand is that the form of ammonia is different in a higher pH than a lower one. Ammonia has two forms, ionized (NH4+) and unionized (NH3), with the latter being more toxic to fish. At a pH of 7.0, most of the ammonia in the tank is in it's ionized form, while ammonia in water with a pH of 8.5+ may have 30% or more in the unionized form. The unionized ammonia should remain below 0.05 mg/l, as there will always be a certain percentage of unionized ammonia even in a lower pH.
Now, the second thing is the biological capacity of the tank. What this means is how much ammonia the nitrifying bacteria can process within a certain time frame and GPH of the filter. Obviosly, the more biological filtration you have the better. If you have inadequate biological filtration, then your need to do w/c's will increase as the free ammonia (due to inadequate bio filter) will cause the fish stress and will eventually lead to a weakened immune system which will cause oportunistic bacteria/parasites to attack. This is the main reason why we have to do so many w/c's is because our biological filtration is inadequate and ammonia builds in the aquarium. Most people use sponge filters in their tanks. They work great when clean for nitrifying bacteria to colonize, but once they begin to filter stuff from the aquarium, they become clogged and actually restrict flow and even reduce oxygen saturation and may cause the aerobic bacteria to become anaerobic, which is bad. Sponge filters need to be cleaned at minimum 2 times a week for optimum filtration. But cleaning that often will deplete the nitrifying bacteria colony. The only way to solve this is to increase the number of sponge filters in the tank, which is increasing the biological capacity. Now, say you have more than adequate biological filtration with a wet/dry filter, you will notice that the water quality will remain much better for longer than using just sponge filters. This is because the wet/dry provides an optimum breeding ground for the nitrifying bacteria and allows the bacteria to process/consume the ammonia into nitrite or even nitrate within one pass. This is ideal for growing out young fry as there are minimal amounts of ammonia in the tank, which reduces stress and encourages healthy growth. Also, the tanks need to be wiped down during EVERY w/c. The slime buildup on the walls of the tank will actually increase the biological load and put more pressure on the biological filter and actually reduce it's performance.
Also, the amount of BH or other food fed at one time also plays a role in the biological filtration/ammonia production. If you over feed and left over food is on the bottom, that food begins to breakdown and ammonia is produced. That will increase the bioload of the tank and increase the work of the biological filter. By feeding only what they will eat in the first few minutes will cut down the chances of food being left over. This will keep the water quality much better and will not produce excess ammonia.
If the above information is followed, it is possible to over stock a tank and be able to still grow the fish out at a good rate. Granted, you will still need to do w/c's regardless of what kind of filtration you use only to remove feces and to reduce the nitrates, which can hinder growth as it is another stress factor for the fish. Personally, I have kept 100 1.5" fry in a 30 gallon tank with only a large wet/dry and by feeding only what they will eat within a few minutes, I only did 2 30% w/c's daily (only to remove fece's and to reduce the nitrate as wet/dry's and similar filters produce nitrate at a much faster rate due to their efficiency). I also cleaned the prefilter daily and wiped down the tank during every w/c. The secret behind stocking at high densities is to have an effecient and effective filter. Now as for people who have a higher pH, yes you will need to do more w/c's than people who have a lower pH due to the unionized ammonia factor. Just like Dan said, what might work for some, may not work for others. This is because of the pH of your water and the biological capacity of you filters. Sorry for rather long (and complex) write up, but this is something that everyone needs to know and is not well known as this information isnt easily accessable to most. It just comes down to the pH of the water and the biological capacity of your filters.

-Ryan

[Barb Newell]

Excellent information, thanks Ryan :)

Barb

[Anonapersona]

This is really interesting, thanks for joining in Dkarc.

So, there are at least three things that are important in keeping healthy discus, or at least in keeping healthy water for discus.

First, is controlling ammonia and of course that relates to fish density as well as the choice of filtration. Because the pH of the water you'll have will make a huge difference in the ammount of ammonia the fish might be exposed to http://aquanic.org/publicat/usda_rac/efs/srac/463fs.pdf the higher the pH the more filtration we ought to have. So, depending on our pH we need to evaluate the type of filtration and probably the turnover rates of that filtration. I wonder if the turnover rates we use can be related to pH?

Second would be cleanliness, wiping down surfaces and removing feces. this one is tough to do in the planted tank but easy in the barebottom tank.

The last thing would be nitrate control, something accomplished by water changes in the fish only tank and supplimented by plants in the planted tank. Maybe that is really what my fish ratio is addressing, for that would explain the difference between bare tanks and planted tanks. Perhaps this is just a poor substitute for testing for nitrate. Hmm, I may try to look into that also. I do recall that Phil mentioned once that he had to increase water changes in the planted tank to control nitrates.



I'll guess that a "large wet/dry" on a 30 gallon tank might be one sized for 100 gallons or better, and containing at least 5 or 10 gallons of additional water. I can't guess at the flow rate you might have for fry but it wouldn't have been too fast, maybe 30 gallons per hour or one tank volume per hour. So, your 100 fry in 40 gallons total water, 2 x 30% WC had a ratio of 100fishx0.5days/.3 changedx40gallons =4.1 for very small fish, with complete ammonia control, excellent sanitation and presumably low pH. But, now I want to know if you tested for nitrate on this tank, and I'll bet you didn't.

Well, sorry to be airing all my thoughts out in public, it is always a learning experience for me, hope it wasn't too boring.

Anona

[Terrybo]

I think the folks with plants are factoring the needs of the plants with the needs of the discus and so have higher numbers (which are less than optimum for discus, but better for plants)

I have always had planted tanks, and the needs of the plants are never my priority over the needs of the discus. I consider the plants as beautiful filters that remove nitrates, and allow me to keep the tank cleaner with fewer water changes. I would also like to add that I agree BB tanks are the way for beginners to go, because the plants only help when they are established and growing heartily with an elaborate root system. When a plant tank is started, there is often lots of dying plants and debris that actually add to the bioload rather than help with filtration.
The bottom line for anyone, whether they have a planted discus tank or BB tank, should be low nitrates.

Terry

[GulfCoastDiscus]

How are things Terry? Call me

dan

[Dkarc@Aol.com]

Anona, the turnover rates of a tank may depend upon the pH of the water, this is something I havent thought about....
The wet/dry filter that I used for the 30 gallon tank is rated for a 55 gallon tank and the turnover rate is 2-3 times an hour. Nope, your right, I never checked for nitrates, except for the first few days after I put them in to determine the % of w/c's that would be needed (I put them in when they were .5"). I orginally started out with 1 30% w/c daily, but as they grew, the nitrates increased due to more ammonia being produced, so I upped it to twice a day. It would never hurt to increase the w/c's even more and I suspect you would see even faster growth (but that is another experiment for me later ;D) I suppose you could have plants in the tank/sump to control some nitrates, but it would depend upon the kind of plant that is used as some are more efficient than others. Now, I know of a gentleman who has a central system and raises beautiful fish, but only does w/c's every 2-3 days. He can do this because he has a denitrification filter that he built himself. The filter will control nitrates and thus put less stress on the fish, which will equal healthy fish. I am planning on setting up a similar system (smaller of course) to use on one of my 30 gallons with a wet/dry and run these experiments again.

-Ryan

[Harriett]

I love the last couple posts on this thread--especially Ryan's longish one. What I see in the needs of my big planted tank vs. my BB 55 gallon grow out tank are very different maintanence schedules to presumably give the same outcome: happy healthy active non-stressed discus. In the planted tank that outcome is delivered because of the large filtering systems keeping ammonia/nitrites non existant and nitrates 5-8ppm: big wet/dry, Magnum HOT, and excellant biofiltering from the plants, along with injected CO2. The once a week maintanence actually assists in creating a stability that is foundational for the system itself to succeed. So 60% water changes and vacuuming 1 x week are working great---. If I tried anything like that schedule in the 55g, my fish would be goners--because THAT system relies on 30% to 50% water changes every 2 days and 2 x day poop siphoning to acheive good results---the 55 runs on an aquaclear and the biofiltering capacity is miniscule compared to the big tank----to compare the 2 diverse methods of discus keeping as though they had identical requirements of maintanence doesn't work---it's almost apples and oranges. You can't very well do 1 x week big water changes in a BB tank and have a good outcome and you would be challenged to change 50% water daily in a planted tank and maintain stability in that system. (because you'd be disrupting nutrient intake of plants/plant growth/ and ulitmately biofiltration, seems to me.)
I Think the BB tank advocates freak when they hear 1 x week water changes, but it is NOT the same system.

Last note---Carol, I respectfully disagree with the post where you stated "I think the folks with plants are factoring the needs of the plants with the needs of the discus and so have higher numbers (which are less than optimum for discus, but better for plants). The goal in a planted discus tank, at least in my hobby and for several other folks I know, is to create an environment wherein the needs of the discus are the highest priority; those needs and the parameters of providing healthful care can absolutely be achieved. The fun and challenge is to create that environment with an esthetic that makes a total knockout picture---I keep both types of tanks, as said, and for me there is absolutely no comparison between looking at a beautiful mature planted and aquascsaped tank with big fat happy discus swimming amongst the plants and driftwood with looking at a box of water with big fat happy discus swimming around in that. With some solid research, thoughtful planning, some knowledgable folks to ask questions of, and some hands on experience, you can make it work. I Know my guys in the planted tank are having way more fun than my grow outs in the bare tank---all I have to do is watch them.
So there's my gardeners' 2 cents, ok?
Best regards,
Harriett

[Anonapersona]

Now, I know of a gentleman who has a central system and raises beautiful fish, but only does w/c's every 2-3 days. He can do this because he has a denitrification filter that he built himself. The filter will control nitrates and thus put less stress on the fish, which will equal healthy fish.

LOL! I got a vision of my next tank! Orchids above, discus below! Oooh, too much! I'll just have to control the humidity...umm, cocoa fiber matting to cover the roots but orchids open to the air in a trough, water dripping thru a spray bar onto the roots and bioballs or orchid wood chunks, then falling into the discus tank with a way to slide the orchid trough over to do maintainence on the fish. Hey, it could work!

[Dkarc@Aol.com]

LOL, it may work. I also know several people down here in FL who use plants as their only source of filtration. They only have a prefilter for the large derbis. The water overflows through an overflow pipe and it goes outside where there is an 8'x4' trough where there are hundreds and hundreds of submersed and floating plants. Their w/c routines are about once everyother month. the only problem is that the mineral content of the water will go down over that time and will cause a pH crash, so they reconstitute the water weekly with an r/o regeneration mix. Works well for them. Although, they dont keep discus, it would be interesting to see how something like that would work in our tanks.

-Ryan

[Anonapersona]

Harriett,

I agree with your view of planted vs BB tanks, I see that the added filtration of the planted tank is worth about a doubling of the time between water changes.

So, if you had a wet/dry and HOT on the 55 you might well get by with 60% twice a week compared to once a week on the planted tank, due to the biofiltration of the plants.

I do wonder about cleanliness in the planted tank, though. do you ever wipe down the walls and do you gravel vac the planted tank?

[Anonapersona]

LOL, it may work. I also know several people down here in FL who use plants as their only source of filtration. They only have a prefilter for the large derbis. The water overflows through an overflow pipe and it goes outside where there is an 8'x4' trough where there are hundreds and hundreds of submersed and floating plants. Their w/c routines are about once everyother month. the only problem is that the mineral content of the water will go down over that time and will cause a pH crash, so they reconstitute the water weekly with an r/o regeneration mix. Works well for them. Although, they dont keep discus, it would be interesting to see how something like that would work in our tanks.

-Ryan


There is still the slime factor with discus... I think that the bacterial concerns with slime may make that different for discus -- but Hey, I don't know, I'm just a novice around here, asking questions and thinking out loud.

I do suspect that if I grew orchids like that I'd have a REAL flying midge problem... now if I could just get the flys to drop into the tank along with the bloodworms....discus will eat flys won't they? LOL

[Cosmo]

Very Very Interesting reading... and I love your logical way of approaching a mathematical solution while acknowledging there are other variables that effect the actual impact of the quantity and volume of WC's... are you by chance an engineer by profession??

Ryan's post highlighted the interaction of the certain parameters of the water chemistry but I don't think he addressed one of the variables Carol speculated about, water softness (which I don't know the answer to either).

I was, however, trying to extrapolate Ann's equation to account for WC's done on a less consistent basis, ie, using myself as an example - sometimes I get either too busy, or too lazy (mostly too busy since I'll stay up later than normal to take care of my babies) to do daily water changes. The past few weeks as I've done construction in the basement I've averaged about 5 WC's per week instead of my normal 7 and can't figure out how to come up with my ratio according to Ann's formula.

10 fish, evenly split between Adult and Juvenile in a 180 gal tank. I figure the decorations and gravel (this is the one in the family room the wife insists be pretty) take up about 20 gals of capacity so I'm guessing 160 gal actual water. Each WC I change approx 75 gal. Ann, since your mind is obviously much more mathematically oriented than mine, could you make the adjustment to the formula and let me know?

Relating to Ryan's input, the water is soft, 100% remineralized RO (I know, I know, you all think I'm crazy), keep it at about 135 ppm and a slightly acidic Ph of 6.4 and have 3 big Eheim's ( 2 X 2217 and 1 X 2229) bio filters with prefilters on the intakes. I'm thinking this water chemistry actually reduces my need for water changes, but I just cant' bring myself to miss more than one day anyway. Would I be correct in this thought Ryan?

Would really appreciate some feedback since, like I said, I am somewhat fanatical when it comes to my Discus so I'm very curious on how this would rate on the Ann and Ryan Index's

Thanks all
Jim

[Dkarc@Aol.com]

Well, if you only have 10 fish in a 180 gallon tank with the 3 eheim's, I think you have more than enough biological filtration. You could probably go a few days without a w/c in the 180 if you only have 10 fish in there. The bio-load isnt very large and if all 3 filters are actively working, then you shouldnt worry about skipping a day or 2. Just be sure to check your parameters frequently for ammonia and nitrate. It shouldnt be very high as like I said, the bio-load isnt very big and for that size tank. If need be, you could go several days (3-4+) without a w/c without any fear of problems as the large volume of water will remain stable.

-Ryan

[Dkarc@Aol.com]

As for Carol's post about the water softness, I would say that you could get by with slightly less w/c's due to the unionized ammonia factor, but you couldnt go several days without w/c's but if it is really soft, the natural nitrification process will cause the pH to crash. Now, if you have really soft water/lower pH in a larger tank (like Jim's), then you could still get by with even less w/c's because a large body of water will remain much more stable than a smaller body of water and so any pH changes will occur much slower. It also depends upon the KH of the water. For example, I have a water hardness of 4 GH and 6 KH straight out of the tap (I know, go ahead and hate me. :P), but I can leave a large tank with no w/c's for a week and only have a .2-.3 pH drop. Doing the same thing in a smaller tank (55 gallon for example) and I can only leave it for 3-4 days before I begin to notice a significant pH drop. Also, it depends upon how much ammonia is being produced. If you havea really heavily stocked tank and feed heavily and have an oversized biological filter (wet/dry for example), then I would have to do daily w/c's, even if I have really hard water as the nitrifying bacteria are much more active and therefore producing much more acid, which will cause the pH to drop or even crash. Also, if I have the same situation, but only have a few sponge filters in the tank, then you will notice the tank water gets cloudy much more easier and you will get ammonia spikes because the biological filter can't keep up with the amount of ammonia produced. This is very common in heavily stocked tanks and the only solution is 1.) increase w/c's to reduce the amount of ammonia and/or 2.) increase the biological capacity. This would be done by adding in more sponge filters or adding a wet/dry to the tank. So, ideally, you would have water that is low in pH and high in buffering capacity (KH), but very few are blessed with this kind of water. So, the only thing we can do is increase the biological capacity in our tanks or reduce the stocking levels per tank.

[Cosmo]

Ryan,

Thanks for the feedback. Got my wife to go along with the 180 by explaining that larger bodies of water are more stable and therefore require less maintenance... just can't bring myself to "take the chance"... personal problem I guess :)

The Eheim 2229 is a wet/dry - think Ann has one too if I remember correctly.. amonia and nitrites always zero, nitrates tend to stay around 5 but sneak up if I go too long without a WC ( I measured the 5 the one time I actually skipped 2 days between changes).

My water is soft, but I add a good buffer so haven't experienced any ph crashes since I started using it (several months now). Before that, was crashing daily. :( but didn't know it cause my little dip stick tester couldn't read that low - found out (to my horror) when I got a digital ph pen that I was in the low 4's instead of the low 6's like I had thought.

thanks again
Jim

PS. Ann, if you get the chance, would really appreciate your help applying your formula to my WC schedule. tks :)

[Anonapersona]

OK, I'll try this, but remember that I am playing with this to keep my mind from decaying, so beware that there could be humongous errors in my thinking!!

OK, oh, this is Hard! I thought I had it, but that won't work...

What happens is that the formula expresses the upper limit of pollution in the tank if you kept the changes regular for long enough for that limit to be reached; it takes several weeks to get there. If you skip a few days, no water changes at all, then you are adding that many fish days to the tank contents at that time, then when you picked it up agian, you'd hope to do a bigger than normal water change to get back on the same path you were on.

OK, 10 fish, 180 nominal tank size, 160 true gallons, 75 gallon water change, skipping 2 days sometimes.
The 75 gal WC is 47% of the 160 true gallons, but in the ratio I'll use the nominal tank size to compare it to what I've been collecting from other people. It'd be just as easy to simply use "days waste" when we are talking about just your tank, the other parts of the ratio are just so I can compare different tanks.

Your normal ratio is (10x1)/(.47x180)=0.118 when you are doing daily changes (my, what pampered fish!)

The ratio, after 2 days with no changes, you've added
(10fishx2days waste)/180 gallons = 0.125

So, 0.118 + 0.125 = 0.243 which is still an excellent ratio, if this number has any real value I'd predict that your fish don't even seem to notice.

Now, it gets tricky. You are beginning with a higher base value. Unless you actually do a larger than normal water change or increase the frequency of the water changes, this increase ought to remain in the tank.

If you did a second 47% water change back to back, on Monday do two changes, for example, you'd be right back to the starting point or very nearly so, as you'd leave 0.53x that level of waste in the tank. To get exactly back to your excellent levels you'd change 0.125/0.243 = 51% =82 gallons or just a tiny bit more than normal on a back to back water change.

It'd be better to just do a larger than normal water change on Monday to get back on track, for that is what we instinctively do I think. On Monday morning the tank has a 0.243 fish-day/gal ratio in 180 nominal gallons or 0.243 x 180 gallons = 43.74 fish-days, or 43.74 x 10 fish = 4.374 dayswaste (just as if you'd filled a new tank with new water and not changed water for 4 1/2 days), by Monday evening that has risen to 5.374 dayswaste.

Since you normally were running the tank with a ratio of 0.118 fish-day/gal = 21.24 fish-days = 2.124 dayswaste you need to remove 3.25 dayswaste from the tank. That is a water change of 3.25/5.374 = 60% or 97 gallons instead of the usual 75 gallons.

Now, I could try to work through what happens if you just went back to the normal amount, but I can't quite reason it out. Oh, yes, I can. I think, not certain though, that you'd maintain that 0.243 ratio as long as you kept to the 5 and 2 schedule. I guess that making an excell spreadsheet could confirm it, but I can't believe I've worked so long on this already!

And yes, I am/was an engineer, you must be able to guess that when you see someone doing this for amusement!
[edited on 9/7 for clarity in the math re: ratio and days of waste calcs]

[Anonapersona]

Oh, this is great! I seem to have mathematically confirmed Ryan's educated prediction regarding not needing to worry about 2 days missed and being able to go maybe 4 days with no water changes if necessary.

And THAT, is what I am trying to do, get a handle on what an experienced person knows!


FWIW, I have a wet/dry but it is not in use yet. The discus tank has a Penguin 330 with a biowheel, and I have a real wet/dry in need of a pump up in the attic waiting for the fish to move around -- when the cichlids move out of the 110gallon, I'll put the discus in there and hook up the wet/dry then. I trying to figure out how many of my fish I can keep between all the tanks in the house, some planted, some driftwood, some bare -- that is the heart of the working out the ratio, so I can figure out how many fish to put into what tanks with reasonable water changes given my 7.9 pH water.

[Cosmo]

Ann,

My mind hurts just trying to follow you... wow, what a mind!
I tried to put it in a spreadsheet, but quickly got lost. If I have any time this weekend maybel I'll try and combine the data in this thread and plot in a spreadsheet - not highly likely I'll have time, but, would be interesting...

Could have swore you'd mentioned having a 2229, but guess it was someone else. I have a "real" wet/dry missing a pump too (given to me) and was thinking of trying to plumb this into multiple breeding tanks w/o creating too much current, maybe even bulkheading to an eheim for output.. still working on the plumbing etc but probably will stick with a straight drip. Went with the Eheim cause they can't overflow... have hardwood floors upstairs where it would have originally gone..

Thanks alot, and please keep us updated on your formula, very very interesting.

Jim