I'm stumped on this one. I've been adding calcium sulfate, potassium sulfate and magnesium sulfate to my tank after doing water changes with RO water to bring the KH down to where I want it. I add these to a jar, shake vigorously and dump it in. Not all of it disperses and "chunks" rest on the bottom of the tank and various plants until it is all dissolved some hours later.
In the course of a day this happened to my Elatine, where coincidentally a lot if the undissolved solids lay during the day.
Is it possible the sulfates could have "burned" the plants? It's not phosphate, I does plenty of that and the temp is a steady 75 degrees.
Rhetorical Question: Why does this sort of thing only happen to the cool plants?