Ok, but there are some with larger dark rust spots on most of the leaves, I have seen java ferns with like vivid green saturation before. this doesn't look like the case. Plus if you can see some of the mini-nana leaves are covered in dark patches also.
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I will try to get a better photo, if it would be diatoms would be all over. The leaves look a little like when you burn the crust of the bread in the oven.
Yes a lot of plantlets, but the new plants have the same spots on them, they don't wipe off.
Doesn't seem like brown algae, will try to get better photos.
The water is acidic, I keep angels and rams