Really not trying to give you a hard time. If you do a 50% WC then you are limiting frets as you have just delete the mix by 50%
I was suggesting getting the right balance of frets not eliminating them completely.
I understand your meaning,point.
If it is Overdosing of ?? as you suggest it might be,and considering nothing has changed in dosing regime according to OP other than osmocote and old, possibly Exhausted? Aquasoil,then weekly water change should compensate for the proposed overdosing of ??
Adding some more plant's would also help in this regard no?
Personally have found that ensuring a little bit of everything,, is far easier than trying to identify what may be lacking, and weekly water change may well take care of any excess that slow growing crypt's are not using.
Cannot say I would be diluting available nutrient's by half with 50% weekly water change, without knowing what rate plant's are using that which I or OP ar dosing.Plant's ARE no doubt consuming some,most? before water change time.