The Puffer Forum

sevenyearnight wrote:I thought the nitrification process lowered the KH, which would/could then lower the pH.

RTR wrote:On the water chemistry I can help most easily, so I;ll digress on that first. In FW (fresh water) that has not been polluted or abused by the use of commercial buffers and such inappropriate materials, KH, alkalinity or carbonate/bicarbonate hardness, is essentially responsible for the water's pH reading. But KH is used up in normal tank processes, especially biological nitrification. Thus it is fully normal for the KH to decline over time since the last water change. All nitrate produced in the tank from ammonia results in the loss of bicarbonate in double the equivalent amount. In unplanted tanks, nitrate increases as alkalinity falls because the chemistry requires the sacrifice of alkalinity in the oxidation of ammonia to nitrate. Routine water changes remove the nitrate and replenish the alkalinity in exactly the percentages used for the water change - changing 50% of the water removes 50% of the nitrate and replenishes 50% of the expended alkalinity. Tanks with heavy algae may show less nitrate, as will planted tanks, as algae and plants require nitrogen and take up ammonia and nitrate (few can take up nitrite, it is harder to handle safely in bio-systems), but the KH is still depleted even if the nitrate reading/titer is low. Removing nitrate by plants or other processes does not in any way remove the requirement for water changes. They are still required equally or even more so by the need to replace all the depleted minerals used by the plants or algae.