# water change



## fish man chan (Feb 6, 2013)

hi all is doing a 90% water change possible with out crashing the bio load ? i have had a mini cycle and nitrate at 80ppm.


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## gverde (Mar 3, 2010)

Why do you want to change that much water? I usually do large water changes weekly. The most I have done is 75-80% with no problems.


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## Spencer88 (Mar 1, 2013)

I would only do like %25 water change every week depending on how many fish you got etc.


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## b3w4r3 (Dec 14, 2012)

fish man chan said:


> hi all is doing a 90% water change possible with out crashing the bio load ? i have had a mini cycle and nitrate at 80ppm.


Yes, you can change that much water without harming your bacteria.


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## fish man chan (Feb 6, 2013)

normaly do 50% water change weekly but mini cycle lasted 12 days so when it was done nitrate was at 80ppm. want to get it back to 10ppm just thought a large water change would be beater than say two 50% changes but not shure ?


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## GTZ (Apr 21, 2010)

How long has the filter/tank been cycled and/or running? What caused the mini cycle?


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## fish man chan (Feb 6, 2013)

tank been running abought 8 weeks. it was totaly cycled (fish in ) . added 3 more yellow labs 2.5" ish . nitrate shot up to 80ppm then i stupitly over cleand the tank and cannister thus getting a mini cycle i think . just done 80% water change and changed the black filter sponge but when i switched the filter back on loads of detrus came out so am thinking that might of been the problem .


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## vann59 (Jun 20, 2011)

The water contains very little BB so large water change isn't what causes a mini cycle, it's probably the way you cleaned the filter. Weekly 25% water changes will only suffice if you have a very light bio load.

Let's say your fish only produced 5 PPM of nitrate in your tank each week, which is really a super small bio load. And you changed 25% of the water weekly. And let's say we are figuring our math starting at a reading of 5 ppm nitrate. The first water change would lower the nitrates to 3.75 ppm.

A week later the nitrate will in our theoretical example be 8.75 ppm since the fish produce 5 ppm weekly. The second water change will leave us with roughly 6.5 ppm (rounded), and a week later it will be 11.5 ppm. The third week our water change will bring it back to 8.6 ppm. After a week it's back up to 13.6 ppm. Change the water and its at 10.2 ppm.

Notice that in a short time your nitrates have climbed to over twice the original level and it will continue to climb because you only remove 1/4 of the new increased level of nitrates each time you do a water change. So you either have to increase the quantity of water you change or the frequency that you do a water change.


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## DJRansome (Oct 29, 2005)

I do 90% without issues. Usually I do more like 75%.


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## fish man chan (Feb 6, 2013)

thanks for the help all


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## DJRansome (Oct 29, 2005)

Sometimes if the fish have become used to the 80ppm (old tank syndrome) over a period of time you are better off doing a series of smaller water changes to acclimate them to the cleaner water. But if it shot up no problem with a large water change.


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