You want something like 3-6x a day feed to avoid issues. My comparison lately is like an engine how it burns fuel/air andraws in fresh air/fuel and repeats. If its not in good order just like an engine, cant really do much without taking apart and re building it. Otherwords you cant. You get build up of salts, minerals, pf buffers and whatelse in the tap water. Bacteria.
Tweaking enviorment can help plant run through its nutes better. Increase air circulation, raise temps. As rh lowers later in flower etc. When ever its just not drying back you still want to circulate fresh solution. Checking ec in runoff helps dial that in, should be within .3 ec from inflow.
I guess its actually really easy to overwater coco and get N tox or locolized N tox. I wouldnt say toxic as I never had issues from that but going from 12x to 6x a day fixed that. I just needed to wrap bags around the pots sealed off so the enviorment dont mess with it and produce rough results. Its working almost 2 wks into flower the leafs never been so perfect light green.
Anyway hope you figure it out. It simply needs more or less and to stay there the ec. From seed new strain can need as much as half the ec. When I did do from seed at the time I didnt learn how to dial in because I just so happened to use a ec in its range. It was 1.1ec at the time. My main pheno needs 1.7ec but a few other strains were fine with it but just had a new strain do 1.2ec.
The rest is just keeping it conditioned with freqency.