i have 2x54 T5HO 26" away from the substrate, using 2 Rena xp2 filters, koralia 1 for circulation and using ada aqua soil.
there were a thread where people have said that extra potassium in their water slowed the plant growth, same applied for the phosphate. am not sure how correct this information is.
I've never seen any evidence of K+ harming growth in anyway, there's no evidence for it horticulturally, till you get to salt stress ranges, which are hundred's of ppm. Many ran K+ in the 40-100+ ppm K+ ranges for about 3-5 years in the USA, no one reported issues then curiously..........
I recall Erik Leung won the AGA contest with his stem plant tank using 100+ K+ ppm without any issues.
I tested about dozen claims of "excess" K+ using all sorts of supposed sensitive plants and could confirm nothing in each and every case.
Correlation does not imply cause. It could be many things.
That said..........I see not reason to dose more K2SO4..........unless you simply are not adding much KNO3. You should not run into a limiting K+ scenario using KNO3. I add GH booster once a week, it's for my low GH tap.......but if you have RO etc, then you may as well blend RO+ Tap, maybe try 1/2 and 1/2, or 1/3 to 2/3rds etc.......add some MgSO4(this can be added at the water change, or mixed in with the Trace mix like PMDD suggested years ago).
I did this for my plants and dosed a fair amount of everything here when I lived in Davis CA which has very very hard tap water, I did a 50:50 split with RO and tap:
I got about 6-7 " per week. PAR was about 120 at the tops of the plants, so that did not help. At 50-70, I only get about 3". This is at the tips of the plants.
Sometimes just leaving things alone can help more than day to day fiddling. I do not day to day fiddle. 2-3x a week is more what I prefer. But this is more my own habit. I'm not impatient.
If you dose good and then leave, there's a fair amount of nutrients.........so things will grow for awhile quite well.........then later...after they ARE GONE, the reserves are exhausted......then you start to have reduced growth..but there's a few days time delay, maybe a few weeks. ADA AS will have a fair amount of ferts also, but reduced N as it ages.........
Also, the last time you trim stem plants also makes a large difference in such cases where you have nutrients in the water, but also the sediment. Much longer time to develop good root systems......
And if there is less in the water...the plants will go after things in the sediments. This will give you some ideas to think about.