I would cut the KH2PO4 in half or less, plants need much less phosphate than they do nitrogen.
If your nitrate is not too high (under 20 ppm) then I would add more KNO3. That will give you more potassium, but still maybe not enough.
If you do not want to add more NO3, then add K2SO4 for more potassium.
I do not really see iron deficiency there.
Leaves that are weakened for example by potassium deficiency are much more easily rasped by snails or Loricariads, so there may be some of each going on.
Agree about the Anubias- 2 kinds of algae on those leaves.
If Excel is available to you you could treat the algae by syringing a little Excel directly onto the worst of the algae. Hydrogen Peroxide works, too. Caution: Most of the recipes you will find for H2O2 are starting with 3%. I understand that 6% is available on your side of the pond. If you are using the 6% I would cut it with water before using it. Might be too strong for the leaves, though it sure would kill the algae!