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Thread: Odd TDS readings.

  1. #1
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    Default Odd TDS readings.

    I guess what I should really be asking is :how do you take tds reading? I always thought you just stick it in your tank and voila! If that's the case, there is something odd going on in my tank.

    My tap water reads 125ppm, my tank reads 250 ppm... it got me thinking so I filled glass of cold tap water last night and today it's at 140ppm maybe it will rise more in next 24h.
    Now here is where things get weird. I filled glass of aquarium water and tested it straight away and magically it's dropped from 250 to 25 in about 20 minutes but I noticed it gets higher when I move the meter then drops back down.
    All I have in there is two "bonsai" trees where wood is just made from plastic and has java fern tied to it, a piece of bogwood and some leftover sand that I was unable to remove completely.
    In my filter, aside from sponge and floss, is just ceramic rings and a bag of peat + a sponge filter inside aquarium.

    Is this a normal occurrence? or is there something inside the tank that's causing such a difference? or is it just higher with higher water movement? of so, would the tds be lower if I lowered water current?
    I don't know what the readings were before I added peat and removed the sand as the tds meter is pretty new.
    So again, am I reading it wrong or is there something wrong with my fish tank?


    Ok, I just tested again and it's at 235ppm? I'm really confused.
    These may seem like stupid questions but it's been a long time since I kept discus and this time I want to understand the technical side of things
    Last edited by Plazuk; 11-01-2017 at 01:14 PM.

  2. #2
    Registered Member Ryan925's Avatar
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    Default Re: Odd TDS readings.

    I have found sometimes you need to shake a tds meter in the water to get accurate readings. It seems sometimes air bubbles get stuck on the end of the probe and causes a false reading. Not sure if that's your situation but that's what I have found
    Im not illiterate...only my phone's auto correct is

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    Default Re: Odd TDS readings.

    It looks like what you are seeing is the effect of temperature. All TDS meters do is measure the electrical conductivity of the water. Then a factor is applied to estimate the TDS. Temperature has a dramatic effect on conductivity.

    Some TDS meters have built-in temperature compensation, some don't. If you want to compare the TDS of cold tap water with warm tank water, you need warm up the tap water so the samples are close to the same temp. I would do that whether the meter has temp compensation or not.

    Also as Ryan said these meters can get a little bubble where the probes are, which throws the reading way off. Shake it in the water to remove any bubbles.

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    Default Re: Odd TDS readings.

    I took the advice and heated up the aged tap water and, even though tds meters thermometer was a bit weird, I showed 180ppm which is what I get from mixing cold and hot tap water but still not 200+ as I get from aquarium.

    Also, just so you know, after a night of sitting on a windowsill, tap water was 140ppm, tank water was 220ppm , both at the same temperature.

    I went a bit further and added some of my dechlorinator. Tds moved up slightly so I went even further and added some epsom salt. Tds went through the roof!! Tds meter went insane showing different readings every second from 809 to 109x10 to -46 and so on =)

    My mystery has been solved. It was the epsom salt I have in my fishtank confusing the tds meter.

    Now that I think about it. Since water straight from the tap in 125ppm and after 24hours 145ppm, is this enough of a difference to be a reason enough to age water? Ph difference in tap 7.4 , after 24f 7.8 .
    Also I took out peat from the filter to see if it makes any difference at all.

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    Registered Member nc0gnet0's Avatar
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    Default Re: Odd TDS readings.

    Quote Originally Posted by Plazuk View Post
    I took the advice and heated up the aged tap water and, even though tds meters thermometer was a bit weird, I showed 180ppm which is what I get from mixing cold and hot tap water but still not 200+ as I get from aquarium.

    Also, just so you know, after a night of sitting on a windowsill, tap water was 140ppm, tank water was 220ppm , both at the same temperature.

    I went a bit further and added some of my dechlorinator. Tds moved up slightly so I went even further and added some epsom salt. Tds went through the roof!! Tds meter went insane showing different readings every second from 809 to 109x10 to -46 and so on =)

    My mystery has been solved. It was the epsom salt I have in my fishtank confusing the tds meter.

    Now that I think about it. Since water straight from the tap in 125ppm and after 24hours 145ppm, is this enough of a difference to be a reason enough to age water? Ph difference in tap 7.4 , after 24f 7.8 .
    Also I took out peat from the filter to see if it makes any difference at all.
    LOL, you never mentioned using Epsom salt in your original post, if you have said so the answer would have been obvious to most. Other than that, Dan was spot on about temperature effecting TDS (conductivity actually). Other than that, only reason for different readings would be additives to your tank water.
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    Default Re: Odd TDS readings.

    Quote Originally Posted by Plazuk View Post

    Now that I think about it. Since water straight from the tap in 125ppm and after 24hours 145ppm, is this enough of a difference to be a reason enough to age water? Ph difference in tap 7.4 , after 24f 7.8 .
    Also I took out peat from the filter to see if it makes any difference at all.
    Marta ,
    1.The main reason for aging water is not TDS at all , but pH swings and dissolved gasses in water AKA Microbubbles during the waterchange. TDS is important only when trying to breed and hatch discus eggs.
    2. Having a PH drop of 0.4 with straight tap I think that you should consider aging at least the half of the WC volume .
    Also , aging water should be performed with water agitation and leaving the water sitting still in a glass may not be as effective as it is with water agitation .

    3. Ive never heard about TDS changes during aging water . Is this normal or should of be considered as a bad TDS results reading ? Anyone ?

    4. Peat should lower the KH , PH and TDS but ussualy it needs some time to do that. With discus tank constant WCs I doubt that peat is able to make any significant change in chemistry.

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    Registered Member Keith Perkins's Avatar
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    Default Re: Odd TDS readings.

    For 4/10s of a point on the TDS I personally wouldn't bother with aging water. I do age mine, but I got into that back when I was breeding them regularly. My TDS actually goes down as my water ages. I live in an area with tons of lime though and if you ever saw the insides of my aging barrels you'd understand why it goes down. I occasionally empty my barrels and haul them outside to remove the lime build up.

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    Registered Member Ryan925's Avatar
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    Default Re: Odd TDS readings.

    Why salt in the tank?
    Im not illiterate...only my phone's auto correct is

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    Default Re: Odd TDS readings.

    I've read you can roughly calculate water hardness using your tds readings here http://www.globalw.com/support/hardness.html
    Using my readings, water in my tap is soft and my aquarium water is slightly hard ( even without the epsom salt is around 200) therefore I was adding soft water to my discus tank only to have it turned harder the next day. That was my reasoning behind ageing water but not the only one. Ph is also an issue. I've read some place that even a 0.3 difference in ph between changing water and tank water can cause stress and I have 0.5-0.6

    I have never had to age my water, I would have to find a thread on here about it but I already got my water containers so it's a start

    Nc0gnet0, I forgot it only hit my when after I checked influence of dechlorinator on tap water's tds

    and Ryan925, epsom salt because white poop.

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    Default Re: Odd TDS readings.

    I already tried to post a reply but something went wrong so if by any chance there will be two similar comments, you will know why

    So, I've read that you can roughly calculate water hardness by using your tds readings here http://www.globalw.com/support/hardness.html
    Based on my tds readings my aquarium water is harder than tap water (even without epsom salt) which means I am putting softer water into my harder aquarium water and that can't be good. That is one of the reasons I was thinking about ageing water the other being the ph. I've read somewhere that even a 0.3 change in water ph can be stressful to you fish and I have a 0.5-0.6 difference.

    I have not mentioned epsom salt because I forgot and it's in there because of white poop problem I'm dealing with.

  11. #11
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    Default Re: Odd TDS readings.

    I bought 20litre water bottles for aging water. It was suppose to be food grade but there is no sign of fork and knife like you see on other plastic food grade stuff. And it smells, not on the outside but the inside, when I opened the bottle I got hit by this super strong, concentrated plastic smell...
    I rinsed it out with very hot water but I don't think it made much difference. I poured cold water to age it and this morning inside of the bottle is just covered with bubbles! Not tiny ones but of fair size. Can I still pour the conditioner in and use it in my tank?
    Also, I read everywhere that you need to have an airpump running in aging water for the whole time of aging and one person even said if you don't it will make the water dead? What does that even mean?
    I don't have a spare airpump or even an access to power outlet where I would age the water...
    Can't I just leave it be overnight without the airpump?

  12. #12
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    Default Re: Odd TDS readings.

    Quote Originally Posted by Plazuk View Post
    I bought 20litre water bottles for aging water. It was suppose to be food grade but there is no sign of fork and knife like you see on other plastic food grade stuff. And it smells, not on the outside but the inside, when I opened the bottle I got hit by this super strong, concentrated plastic smell...
    I rinsed it out with very hot water but I don't think it made much difference. I poured cold water to age it and this morning inside of the bottle is just covered with bubbles! Not tiny ones but of fair size. Can I still pour the conditioner in and use it in my tank?
    Also, I read everywhere that you need to have an airpump running in aging water for the whole time of aging and one person even said if you don't it will make the water dead? What does that even mean?
    I don't have a spare airpump or even an access to power outlet where I would age the water...
    Can't I just leave it be overnight without the airpump?
    Marta you'll have to make some movement to the water surface to stabilize the PH and outgass the water in your aging barrels/ bottles .
    By just living it sit still it will end up just half or non aged meaning not outgassed and PH not stabilized . It won't make the water "dead " but you just won't fully accomplish the purpose of aging it .

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    Default Re: Odd TDS readings.

    Hello people!

    I'm new to the forum and it's my first post but I've been reading and you guys have such amazing info.
    I need a little help with both my tanks though....
    My first tank is a 10 gallon, it has some 2 shrimp, 1 rubberlip pleco, 1 neon tetra (only one that survived), and 2 danios
    I tested it today and it read 1-2ppm for ammonia, 0 nitrates, .50-1ppm nitrites, and PH likes to play around 6.4-7

    My second tank has 4 shrimp, and 1 danio
    It reads 0 for everything

    Can you guys help me out on the situation and or stages of the cycle?

    (I've been using Stability by Seachem for helping out feed the bacteria for the past 3 days)

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