Lava Rocks?

[Byron]

You will kill this plant with an iron-only fertilizer. Java Fern being slow growing requires minimal nutrients, and the other micro-nutrients are as important as iron and all of them need to be balanced. If you need supplementation, Seachem's Flourish Comprehensive Supplement for the Planted Aquarium or the near-identical Brightwell Aquatics' FlorinMulti are your best options. You are in the US so either of these are available; there may be European counterparts I am not aware of.

 

[Stan510]

Ferns love iron. They thrive on it..aquatic or terrestrial ferns. Flourish has iron,and I would not doubt its the iron that does most of the work in that bottle. I say skip the small portions and get the pure Iron Gluconate in Seachems iron.
Look at any fertilizer for ferns and acid loving plants..iron is the main chelated ingredient.
I grant you Flourish may fit the bill on a newly set up aquarium. After that?..just go to iron as the algae proves that in any aged aquarium phosphates and nitrates are in abundance.
I haven't seen Aquarium Co-Ops formula they call easy green and claim better than Flourish. It's probably got a higher amount of iron then Flourish.

 

[vanalisa]

I don't like to iron so almost all of my clothes are the non-wrinkling type.

 

[Retired Viking]

I am happy with flourish at 1/2 doseage but as my tanks age I will keep all this advice in mind. Thank you.

 

[Stan510]

Every tank varies. And even one tank can vary. My aquarium has fluctuating high light levels depending on the season. That means less ferts is fine in winter and when the days are longer like now,I watch for the signs of faster growth.
But Flourish is much better than plain tap water for the plants.