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Results 1 to 10 of 22
  1. Default A Note on Nitrate and Water Changes


    1 Not allowed!
    Being a mathematician, I decided to do a calculation (I'm not kidding when I say I have a notebook with just formulas and calculations I've written pertaining to my aquarium) to figure out the relationship between water changes and nitrate levels in the tank. I'd like to share what I've found because it's rather counter-intuitive and I think quite a few people would benefit from it.

    Some thing's I've read (here and on other sites) make such claims as, "If you don't do at least 50% water changes every week, you won't be able to overcome the weekly nitrate production and the levels will continue to rise indefinitely, leading to a tank crash." Well, I bring good news: these claims turned out to be false. I'll explain the actual relationship using as little math as possible so everyone can understand.

    Let k be amount of nitrate produced in your tank in one week, let p be the proportion of water that you change during a water change (NOTE: since this is proportion and not percentage, a 25% water change corresponds to p = 0.25, and similarly for other percentages), and let n be the number of weeks between water changes. As time goes on, the nitrate concentration in your tank will approach the value n*k/p (call this number L for future reference). Of course, this model is simplified, but I think it'll work perfectly fine for all intents and purposes. Depending on whether your nitrate levels are currently higher or lower than this number, they will either decrease to it or increase to it, respectively, over time.

    I'll do an example to illustrate how the formula works and even how you can figure out a water change schedule that works for you and that results in an acceptable nitrate concentration over time. Let's say your tank produces 5ppm of nitrate every week and you change 50% of your water every other week. This means that k = 5, p = 0.5 and n = 2. Using the formula, we see that L = 2*5/0.5 = 20. Therefore your tank will approach a nitrate concentration of 20ppm as time goes on (and never increase past this).

    Now, if you want to figure out how often and how much to change your water, use the following method. We'll be using the equation L/k = n/p, which is just a rearrangement of the one above. First, choose your target nitrate concentration (e.g. if you never want your nitrates to go above 20ppm, then your target nitrate concentration is 20) and plug this in for L in the formula. Because you also know k, you can just find an n and a p that make the equation work (there are usually multiple combinations, so you'll be able to find one that works for you). Let's do an example. Let's say I never want my nitrates to go above 10ppm and my tank produces 5ppm of nitrate per week. Then we have 10/5 = n/p or 2 = n/p. Now, some pairs of n and p that work are (0.5, 0.25) (1, 0.5), (2,1) (n is the first number and p is the second; also, there are many more pairs but these are impractical because they would require more than two water changes per week). These tell me that I can either change 25% of the water twice per week, 50% of the water every week or 100% of the water every 2 weeks (though that's not recommended, it will work mathematically). Just make sure that the p is never above 1, because p = 1 corresponds to a 100% water change.

    If anyone has any questions, or wants me to do a calculation for them if they're not comfortable with their math abilities to do it themselves, just let me know; I'd be happy to help.
    Joseph Granata
    My current 37gal freshwater community tank journal: http://www.aquaticcommunity.com/aqua...d.php?t=116054
    My upcoming 37gal FOWLR tank journal: http://www.aquaticcommunity.com/aqua...42#post1214342

  2. Default


    0 Not allowed!
    Design a calculator to figure your formulas.

  3. Default


    0 Not allowed!
    I have negative idea how to even begin doing that. Me and computers don't get along very well. I'm old fashioned; I prefer the trusty pencil and paper to technology any day.
    Joseph Granata
    My current 37gal freshwater community tank journal: http://www.aquaticcommunity.com/aqua...d.php?t=116054
    My upcoming 37gal FOWLR tank journal: http://www.aquaticcommunity.com/aqua...42#post1214342

  4. #4

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    Default


    3 Not allowed!
    Water changes aren't just about nitrates. We often use nitrates as an indicator but water changes are also done to remove hormones and replace trace elements among other things. People are always trying to reduce the amount or frequency but what it all boils down to is fish need clean fresh water as often as you can give it to them, not as little as you have to.
    When I go fishing I just place a sharp rock in the water and sit there waiting for all the dead fish to float to the top... Kingfisher
    Brutal honesty will be shown on this screen.
    I think my fish is adjusting well to the four gallon, He's laying on his side attempting to go to sleep on the bottom of the gravel.
    Tolerance is a great thing to have, so is the ability to shut up.

    I can explain it to you, but I can't understand it for you.


  5. Default


    0 Not allowed!
    I completely agree. I posted this more so that people would just be able to understand the relationship between nitrate levels and water changes and know what to expect based on their water change schedules.

    I assumed that if they decided to use it to come up with a water change schedule that works for them in terms of nitrates, they would also be mindful of other constraints such as those you mentioned above, but thanks for mentioning it for people who may not have thought of that
    Joseph Granata
    My current 37gal freshwater community tank journal: http://www.aquaticcommunity.com/aqua...d.php?t=116054
    My upcoming 37gal FOWLR tank journal: http://www.aquaticcommunity.com/aqua...42#post1214342

  6. #6

    Default


    2 Not allowed!
    Joseph,

    1. I don't get it
    2. Seems to be a theoretical formula, or did you test to confirm?

  7. Default


    0 Not allowed!
    Well I started off theoretically but I checked it against my nitrate levels over the past two years (I keep an aquarium log) and they were all in line with what the formula would predict
    Joseph Granata
    My current 37gal freshwater community tank journal: http://www.aquaticcommunity.com/aqua...d.php?t=116054
    My upcoming 37gal FOWLR tank journal: http://www.aquaticcommunity.com/aqua...42#post1214342

  8. #8

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    Default


    0 Not allowed!
    If the issue is the math of diluting out something toxic in the water (ammonia, Nitrite, nitrate) the math really doesn't need to be that hard and you don't have to really go into variables.

    If your reading is (for example) 1ppm, and you take out 50%(half) of the water and replace it with water that doesn't have any, then you end up with a reading of half of one... or 0.5ppm

    So take the reading you get on your water.
    Determine how much water you are going to have left after your water change (100% - the percent you are changing)
    Multiply your reading times the percentage of water you have left.

    Is this number in the safe range?

    If yes, then you are changing enough to dilute the toxins.

    If no, then you need to change more.

  9. #9

    Default


    1 Not allowed!
    Quote Originally Posted by jgranata13 View Post
    Some thing's I've read (here and on other sites) make such claims as, "If you don't do at least 50% water changes every week, you won't be able to overcome the weekly nitrate production and the levels will continue to rise indefinitely, leading to a tank crash." Well, I bring good news: these claims turned out to be false.

    These tell me that I can either change 25% of the water twice per week, 50% of the water every week or 100% of the water every 2 weeks (though that's not recommended, it will work mathematically). Just make sure that the p is never above 1, because p = 1 corresponds to a 100% water change.
    I'm confused by these two statements in your post. You began by saying a 50% water change is not necessary, but at the end your math shows 50% water changes.

    You didn't go into the other factors that contribute to nitrate rises or reductions like bioload, plants, filtration, feeding, etc. so the blanket statement of percentage of a water change needing to be 50% weekly is not correct. Each tank is different and therefor must be treated in its own unique way according to what is happening in that tank.
    Steve
    50 Gallon -
    Endlers | Guppies | Blue Eyed Rice | Celestial Pearl Danios | Threadfin Rainbows | Peacock Gudgeon | Bronze Cory's
    Albino Cory's | Nerite Snails | Ghost Shrimp

  10. Default


    0 Not allowed!
    I was refuting the part about nitrates continuously rising over time and never stopping. For example on an aquarium that produces 5ppm of narrate per week, you could do a 20% weekly water change and your nitrates would never rise above 25ppm AS LONG AS the rate of nitrate production doesn't change.

    Also, When I say rate of nitrate production, I don't only mean the nitrates that are produced from wastes, I mean the change in nitrate over a week, which takes into account all factors that affect nitrate levels. For example, if you have plants, you weekly nitrate production will be less than if to didn't. The impractical part of this model is actually FINDING your tank's specific level of nitrate production, since it's hard to do that without lab equipment.
    Joseph Granata
    My current 37gal freshwater community tank journal: http://www.aquaticcommunity.com/aqua...d.php?t=116054
    My upcoming 37gal FOWLR tank journal: http://www.aquaticcommunity.com/aqua...42#post1214342

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