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Thread: Water change schedule

  1. #1
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    Default Water change schedule

    I was doing 30% water changes every other day but lost one of my fish to a bacterial growth on its face. I’m now doing every day. 1 day 30%, 1 day 50%, etc. Does that seem like a good schedule? More % each day or good like that?

    thanks!

  2. #2
    Moderator Team LizStreithorst's Avatar
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    Default Re: Water change schedule

    That should be fine as long as you don't have juvies and don't have a planted tank with substrate.
    Mama Bear

  3. #3
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    Default Re: Water change schedule

    I do have some 2 1/2” juvies and my tank is planted.

  4. #4
    Registered Member bluelagoon's Avatar
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    Mervin

    Default Re: Water change schedule

    How are you deep cleaning your substrate with plants. Where bacteria and parasites get lots of nutrients to thrive. Hence bacteria infection on the face. 2.5 inch fish have never seen this type of tank before you bought then and takes a while for them to build up a good immune system. All the heavy feeding and WC's will be a lot easier to grow them out some first before the plants. With lots clean water they should almost never get infections. So, this has been my experience with large frequent WC's. By the way always wash your hands just incase you have pathogens on them so you don't cross- contaminate like we can with each other. I know a lot of folks don't. That can happen.

  5. #5
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    Default Re: Water change schedule

    I read some time ago on this site a member had mathematically computed how partial water changes
    are not really totally effective.Simply, he stated if you do an "x" amt of w/c, say 50% you are still leaving
    50% of the pollutants in the water and it will keep building up.
    Now I know I simplified on my part, what he was stating but common sense would tell you that is what's is going on.
    So that's is why I do a 95% plus every night which I know is not perfect, but it's a trade off to having them
    flopping around and being stressed out.
    So bottom line, rethink 30 or 50% w/c.
    Jay

  6. #6
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    Don Speers

    Default Re: Water change schedule

    If you are curious the steady state concentration of a given substance/pollutant is described by the formula Steady State maximum (just prior to water change) = daily production x time in days/fractional water change as decimal (e.g., 50 % = 0.50; 20% = 0.2). Bottom line, you always reach a steady state after a variable number of water changes, you do not infinitely accumulate a pollutant (something I found counterintuitive), but the accumulation can be significant. For instance, 5% water change every 12 hours would result in a given substance such as nitrates increasing by a factor of 10 (reaching steady state after 293 water changes) whereas 90% daily would accumulate by a factor of 1.1111112 and reach steady state after only 5 water changes.

    The point of this for me was to try and compare different volumes and time periods to see what the notional values would be, not to accurately predict real world results. The assumptions are that pollutant increases are steady state and there are no processes removing the pollutant. Both assumptions are frequently invalid in the real world.
    The other observation was that equivalent water changes e.g., total amount of water changed over a given period will result in the same maximum concentration at steady state. For example, change 25%/day your steady state concentration would be the same as 50% every other day. What varies is the concentration just after water changes. This even applies if you change 100%, which in the above case would be every 4th day. Again, I found this counterintuitive, but the math is rock solid.

    This was an exercise that for me applied to a tank with adult fish with mature immune systems and a UV filter. Although for nitrates, you get the same maximum concentration changing 25% every 6 hours as 100% every day, your bacterial counts will be much higher in the first case as bacterial doubling times are not a simple arithmetic increase.

  7. #7
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    Don Speers

    Default Re: Water change schedule

    By the way the above was nothing more than a FYI from the person (or at leastone of them) that did the messages long ago about the mathmatical relationship between volume, frequency, and solute concentrations, but does not apply to this specific situation. For juveniles I completely agree that daily 90%+ water changes in a bare bottom tank is the way to go to maximize size, appearance, and health. Everything I have read supports that. Given my disabilities, my interest in raising juveniles is very low at best.

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