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Math Help - What percentage of water am i changing?

  1. #1
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    What percentage of water am i changing?

    Hi Everyone, would really appreciate it if you could help me out with the below problem. I aint no maths genius, so bare with my pre-school knowledge(aged 28!).

    This is to do with changeing water in a fish tank.
    I have a 300L tank which requires 10% of water changing weekly. This is done by removing 10% into a bucket and then adding 10% of fresh water back into the main tank. So, based on that, my tank would be 90% clean.

    This is the complicated part.
    I have seen a product on the market which is causing me much confusion as to how clean the water would roughly be.
    Again the tank is 300L. The product is a 30L tub which will be filled with clean water. This water circulates with the main tank of water, so effectively, the tank is a total of 330L. After an hour, this 30L tub of water will be thrown away and the water change would be complete(back to 300L tank).
    Based on that what would my;

    water change percentage be =
    What percentage of the tank would be clean =

    The main problem for me is the fact that the 30L of water is getting diluted in the main tank before the dirty water is taken out.

    Thanks for your help

    Andy
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  2. #2
    MHF Contributor
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    Re: What percentage of water am i changing?

    After you add a 30L tub of clean water, the percentage of clean water is 30/330 = 1/11, which is a little less than 1/10. After the tab is removed, the percentage of the clean water stays 1/11 since the water has been mixed thoroughly.
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