Black patches on my java fern?

Question

I bought java fern about 5 weeks ago. When I purchased it, the leaves were all green. Now 5 weeks later, all the leaves exept one new bud have black, brown patches on them, like they are all decaying. (8 of the 9 leaves)

The water parameters are good. Light is 1 watts per gallon and also get 2 hours of indirect sunlight. The fish are 2 bolivian rams and 6 rummynose tetras. It has a diy co2.

The brown Patches are NOT SPORES. It is not circular spots/dots but are random patches all over the leaves.

The java fern has been grown submerged and NOT IMMERSED.

I use only rainwater for my tank.

It it nutrienrt deficiency?

I thought java fern was a very hardy plant, not requiring fertilisers. I thought it would grow fine with just the fish poo. In the same tank, I have java moss which seems to be thriving, making a pretty carpet. What is wrong with my java fern?

Answer 1

The rainwater could very well be the problem.  Java Ferns are hardy, but they cannot survive in nutrient, and equally important, mineral free/low water.  Rainwater has virtually no dissolved minerals, and both plants and fish (even acid loving fish) require things like calcium and magnesium in their water.  I would strongly suggest using a combination of tap water and rainwater, and occaisionally dosing some fertilizer (Flourish, Flora Pride, etc.).

Answer 2

the plant is producing more plants baby ones will slowly appear and drop off had this a number of times looks like dying of then comes to life