Re: Help with high nitrites but falling nitrates
#2
Nitrates shouldn't be falling as there is no mechanism for that to happen. It's more likely that the high nitrite level is interfering with the nitrate test.
Nitrites can climb very high, usually well above the limit of the test so they can be falling again but you can't detect the drop as it takes a while to fall low enough to be within the range of the test kit.
Check your pH and also kH if you have a kH test. It's likely that kH has depleted (it is used by the bacteria) which will have caused a pH drop and will have stalled the cycle. The filter bacteria can't function without carbonates (kH). If this is the case then do a large water change to replenish kH and reduce the nitrite level, then carry on dosing as before.