[plantbrain]

Ditto on CO2.
If there's PO4/ and most of the others, then that is always suspect.

CO2 often gives a false positive(test show more than is actually there) so some addition should likely take care of things and also giving a good critical look at it over time.

You mentioned everything BUT CO2.

Besides light, CO2 will slow everything else down if there's less and this is very often the case.

If anything seems funny and not obvious, do a water change, re set the nutrients and then make certain you have enough CO2.

Regards,
Tom Barr

 

[plantbrain]

If it's a DIY system, ALWAYS suspect CO2.

The test kits can give more CO2 than actually is there due to acid influences, stray electric current(if you use a pH probe), never the reverse.

So you always will have less, not more CO2 than you think or else the right amount(test are accurate).

Regards,
Tom Barr