20 gal tank - good mix of community fish ?

Last Sun June 12, 2016  mixed substrate, also I have to do 50% water change anyway. The landscape was rearranged so the left bottom corner is not covered  at all.
The changes did not affect Cardinal Tetras behavior - they still hang around in the corner.  One fish - the bravest/most curious - visits all parts of the tank while others stay in the corner and come out only during the feeding and the night time. I think I'm done with the experiments, Cardinal Tetras will have to accept their new home as it is. Later I put the tree house to the left front.

The spot on the leaves can be rubbed off, so this is not mineral deficiency signs, I think this is Diatoms. 
The Amazon Sword has net-like leaves (the flesh between the "veins" are missing) so it might point to the Potassium deficiency. I'm starting to think about explicitly providing food to the plants - use Seachem Flourish Potassium + Nitrogen + Phosphorus +  Excel (carbon supplement). 

What do you guys think about messing with Seachem Flourish product line?

Here is my tank as of Sat June 18, 2016, during Cardinal Tetras morning feeding time