changing water

[marinakid]

can anyone enlighten me about how actually changing water reduce nitrate? i mean it will reduce but in fact not significant if it is already low. for example, a tank with 20ppm of nitrate. a water change of 20% will maybe take away 4ppm. i guess a weekly change of 20% maybe not be able to cope up with the bioload in a tank even if it is very lowly stock.

[comycus]

You have answered your qn partially. A given % wc will result in a proportionate % reduction in nitrates. A 20% wc for a tank with 100ppm will reduce nitrates by 20 but only 4ppm for a starting nitrate of 20ppm.

If your bioload is low, you can maintain/reduce your nitrate levels keeping all factors equal. If your bioload is high and your wc is unable to export nitrates out at the same rate of nitrate production, then yes nitrates will keep increasing if you don't do anything about it.

This is the reason why maintaing low nitrates get increasingly harder as it gets lower because your bioload will 'produce' a certain amount of nitrates. You can solv this by reducing the number of fishes or consider the various methods of nitrate reduction like denitrator, dsb, refugium, vsv to name some.

[imcosmokramer]

well, during your waterchanges, you should be siphoning out "junk" as well, so that you have a cleaner tank. This, in the long run, will help with nitrates