I asked a similar question to this about 6 months ago. I enquired if anyone knew at what level potassium started interfering with calcium uptake.
Tom Barr gave me this reply:-
"Not that Ca++ issue again, Erik and myself both tested that notion to 75ppm for myself and Erik had like over 100ppm K+ and we both used the test plant that is suppose to be sensitive, Ammannia gracilius.
Now my plant grew great, his central theme plant won the AGA contest for that year..............
If it was K+, then why did we not have the same problem?
We both had lower Ca++ levels as well so that would error toward the notion that high K+, caused Ca++ blocking.
Ca++ blocking simply does not exist in this context, something I know and can easily justify with repeatable results as well as many folks maintaining very high K+ levels for over a decade.
I'm not saying what those folks claimning it were having, could be poor CO2, NO3 etc.
But I do know it was not high K+ blocking Ca++.
K+ over 100ppm might be bad, but no one has shown it causes issues in planted tanks directly.
K+ can cause salt stress in plant at a certain point, but that is rather high levels, beyond 100ppm.
Folks that use K2SO4, KNO3, and Seachem EQ heavily may have quite high K+."
Hope this helps answer at least part of your question.
Today I just realize, A big mistake, A was dosing full shot of potasium sulfate on top of my KNO3 and KH2PO4 and some K2S04+ TRACE and I just forget to take in consideration the K in KNO3+K2SO4+KH2PO4.
OUPS! That going on for a couple of months
Some observation related or not??? :
• Litle Low in magnesium GH 100 to 120/KH 4O
• Elodea top slow growing, I think probably difficulty with iron intake + I have another bunch of fast growing plant going crazy (probably competiting wit elodea for iron) (I will find the name)
• I’m so scare I have to double dose my phosphate for some time now
My phospate test is a low resolution Hagen (work with a drop of KH2PO4)
I need to change I think I go with Seachem
All the other plants looking at their best from the initial setup a year and a half ago.
Joy, Joy, Joy
Good news What I think was the black spotted algae and other algae seem to diseappear. No more free Lunch