Hate to be cliche but everyones tank is different and I or anyone here could tell you how much you should actually be dosing. I would suggest, finding an accurate ph drop. If you aren't achieving atleast 1ph drop without fish stress, that typically means circulation is an issue. Lack of co2 will/could/can show the same fert like deficiency symptoms. The amount of co2 will typically be judged by the amount of light your pushing. Sorry if my reply is of no help
I appreciate the co2 concern but I was getting 1 ph drop for months when my gh
(and kh) was high. 7.6 down to 6.6. Same issues. I also have a powerhead to make sure there is strong flow even at the opposite end of the tank's outflow
As for recently, the drop checker is always a light green after a few hours of my ph sitting at 6.6.