Is that right before a water change? How much are the nitrates increasing between water changes?
Think of it this way:
If you have nitrates of 30ppm then do a 25% water change the nitrate value (assuming 0ppm in new water) will be ~23ppm. Then at the next water change the nitrates are 33ppm (increase of 10ppm per week) and you again remove 25% of the water it will reduce to 30ppm. So you end up with
First value shows the pre-water change level and the second is the post water change level
week one 30ppm 23ppm
week two 33ppm 25ppm
week three 35ppm 26ppm
week four 36ppm 27ppm
As you can see you there is an accumulation of nitrate in the water over time. This indicates that there are other things accumulating over time as well that are harder to test for such as hormones. IMO its best to adapt water changes to the amount of nitrate in order to attain a given post water change value, I aim for less than 20ppm, but never to less than 25% change.
So for example given a 5ppm per week increase:
The first value is the pre-change level, the second is the % change and the third is the post change level
week one 30ppm 40% 18ppm
week two 23ppm 30% 16ppm
week three 21ppm 25% 16ppm
week four 21ppm 25% 16ppm
Hope that was understandable.
