Some notes on that survey...
The general problem was dying crinkle tips going down on Ludwigia. Smaller close node tips and slow growth on Elodea, rotala stop growing.
1— When ph go over 7.4 problem arise ( due to relation elements absorption/ph relation????)
2— Phosphor, Boron, Zinc, Copper, Manganese, Iron, absorption can be diminish.
Boron is the more immobile element and can bring or resemble Ca intake problem...
3— Kh is not a problem (only is relation to PH)
4— High GH seem to be related to the problem (Maybe higher MG or CA)
5 — Higher Ca and MG related to the problem
6 — NO3, PO4, Potassium and water change do not seem to have any effect on this problem.