K+ does not inhibit Ca uptake in aquatic plants, there's absolutely no evidence in the research or otherwise that this was ever the case
It's that simple.
Furthermore, having done mulitiple test and having maintained 40-60ppm K+ ranges for a decade with 200 species of plants and dozens of local SF aquarist, we never saw anything we could attribute to excess K+.
Ever.
Erik Leung won the AGA contest with over 100ppm K+ and Ammannia gracilius stand was his main theme plant, one often touted as being sensitive to K+ and Ca issues.
This is plainly a myth, take note and do not suggest myths, they have a way of sending people off to bad path to nowhere and never resolve the real issue. It waste everyone's time.
Correlation does not imply causation. What you are seeing is not Ca inhibition nor excess K+.
That much is painly clear.
Note, I did not say what is was, merely what I know it is not.
Ca:Mg ratios, these would have to incredibly unbalanced for a negative growth pattern to occur. This is well known in terrestrial systems.
Generally, folks lack Mg if anything and attribute that to excess K+ for some odd reason. When you increase K+, that often increases uptake of other nutrients such as NO3/Mg/CO2/Traces etc.
You will never find the answer looking at K+ and assuming excess levels are bad. No one ever even thought of excess K+ issues till recently and only because of correlation, we have been dosing excess K+ and have been very successful for a decade prior. So if excess K+ was really the causative factor, we would have seen over 10-15 years ago but we didn't.
This means K+ is not the issue and some other thing is occuring that is giving you the issue.
I add excess K+ and have for 15 years yet I have never seen the symptoms. For the theory to hold true, I would have to be able to replicate the effect under similar Ca/Mg/K+ conditions but to date, I nor anyone here with both hard, med and soft water has not.
So bark up another tree.
This is precisely how myths get started.
Regards,
Tom Barr