Bill Smith Posted July 22, 2020 Share Posted July 22, 2020 Hi: I am considering setting up some water changes with overflow drainage. But I don't think the math is as simple anymore when I'm trying to figure out the percentages of water changed. For example: If I know that I can fill the tank in 20 minutes with a certain flow rate, I normally would assume a 50% water change would take 10 minutes. But since I am not draining the water first (but instead letting the excess overflow) the new water I'm adding will mix with what's there before it overflows. So how do I get to 50% in this model? How long will I run the water to make a 50% water change? Is there a calculation for this? Thanks! Bill Link to comment Share on other sites More sharing options...
Daniel Posted July 22, 2020 Share Posted July 22, 2020 You could measure something like nitrate and see how much water changed it takes for the nitrate to drop 50% and that would give you the amount of water to change. Or some other proxy variable. 1 1 Link to comment Share on other sites More sharing options...
DaveSamsell Posted July 22, 2020 Share Posted July 22, 2020 37 minutes ago, Bill Smith said: Hi: I am considering setting up some water changes with overflow drainage. But I don't think the math is as simple anymore when I'm trying to figure out the percentages of water changed. For example: If I know that I can fill the tank in 20 minutes with a certain flow rate, I normally would assume a 50% water change would take 10 minutes. But since I am not draining the water first (but instead letting the excess overflow) the new water I'm adding will mix with what's there before it overflows. So how do I get to 50% in this model? How long will I run the water to make a 50% water change? Is there a calculation for this? Thanks! Bill Bill, Am not sure. One would have to know how well the new water is actually being diluted & redistributed in the water column. Many variables there. Perhaps one way might be is to keep measuring your Nitrate levels until you see a 50% change. That way, you can then estimate the volume of water that was physically exchanged. 1 Link to comment Share on other sites More sharing options...
DaveSamsell Posted July 22, 2020 Share Posted July 22, 2020 3 minutes ago, Daniel said: You could measure something like nitrate and see how much water changed it takes for the nitrate to drop 50% and that would give you the amount of water to change. Or some other proxy variable. Daniel, I think we were on the same wavelength there. You were typing when I was. Same idea. 😂 1 Link to comment Share on other sites More sharing options...
Daniel Posted July 22, 2020 Share Posted July 22, 2020 Just now, DaveSamsell said: Daniel, I think we were on the same wavelength there. You were typing when I was. Same idea. 😂 My first thought was that it would involve calculus, but I don't think I remember any☺️. Link to comment Share on other sites More sharing options...
DaveSamsell Posted July 22, 2020 Share Posted July 22, 2020 1 minute ago, Daniel said: My first thought was that it would involve calculus, but I don't think I remember any☺️. I had two years of integrated, differential & statistics. Way too many numbers. 😅 Link to comment Share on other sites More sharing options...
Bill Smith Posted July 22, 2020 Author Share Posted July 22, 2020 LOL I came to the right place! Also found this calculator: https://www.hamzasreef.com/Contents/Calculators/EffectiveWaterChange.php I will also try the nitrate check as a way to check the calculator. I have the API test kit, which is a little more precise, and if I do it across 3 different tanks, that should give me a close enough figure. Thank you! Link to comment Share on other sites More sharing options...
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