I noticed recently that the leaves of my Diofformis are closed (or cupped?)
Could they be receiving too much light? I have one compact fluorescent at 36
watt and a single 4" fluorescent tube of 36 watt over 15-gallon of water.

From the dark green of the leaves I am sure they have enough iron. I use a
thin layer of Sera Floredepot as substrate fertilizer and doze Seachem
Potassium & Traces every 3 days. I drop Dennerle iron tab every 2 weeks.

I also have Hygrophila Polysperma and their leaves look wrinkled but they do
grow vertically....