What happens if you add more and more plant biomass, then the NO3 decline?

Hardly any more plant growth/biomass addition.

What happens if the plants really get limited via N?
They cannot take up NH4 either................they do not produce as much O2..........bacteria also do not take up as much NH4 to covert to NO3.........

Get in there and prune and/or add more CO2/NO3/PO4 etc.

Excel ought to kill what's there.
Clean your tank often and especially after disturbing the sediment.

Careful with Engineer and Biologist comments, I'm both


Regards,
Tom Barr