Hey, thanks for the comment, sorry the late reply.

I know this is very basic information, but the role of the biofilter is to brake down ammonia from the fish into nitrite then into nitrate that the plants can use, as your system develops over years(~1+) it gets more and more complex and starts to give your system access to more complex nutrients. You can also starve some parts of the biofilter for oxygen, this can lower the nitrate value to create a more even N-P-K value if you will, ie. from 20-5-5 you can get closer to 5-5-5 as some plants needs less nitrate to produce flowers and fruit. However growing lots of greens in your system would also take up more nitrates i.e. also reducing the nitrate. I can’t remember all the details, i need to re-read some articles first.

I will put it on my list to improve this article at a later date. Thanks