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I've got a Java fern with these weird black spots on the top of its leaves, and honestly, I'm stumped. Can anyone give me a clue what's causing this or how to stop it from happening?

Got any pics? Black spots on top of the leaves is weird, usually it's the underside that gets them, and those are usually seeds. Do you use any ferts on that fern?

I'm using Seachem Flourish, iron, and CO2. Can't get a pic right now, sorry.

Given the plant's requirements are pretty low, I'm inclined to rule out nutrient deficiency or co2 lack. Intense light might be causing burns, or it could be rot from a dying rhizome. Is your Java fern planted in substrate, or is it tied to decor/wood?

It's tied to a piece of driftwood and gets 8 hours of light, but I only have one low-watt bulb. There's duckweed covering the surface, though. It also gets some indirect sunlight from a window.

Honestly, I'm stumped. If you can get a picture up, that might give us a better idea of what's going on.

Here's what it looks like on one of the leaves. I've got another java fern that I grew from a rhizome cutting of the affected one, and it had black spots so bad I had to trim it off.

I'd suggest stopping the iron additive for now. Given that you're using Seachem Flourish, it likely already contains sufficient iron for your planted tank. Excess iron can indeed cause problems, either directly or by hindering the plant's ability to absorb other essential nutrients. The black spots could be an indication of this.

As a shade plant, Java ferns are probably not too fussed about light, so that's unlikely to be the issue. However, I do wonder about your CO2 setup. Are you using a diffused CO2 system or something like Excel?

I'll stop adding the iron, I only dose it once a week anyway. I was also thinking it could be a micronutrient deficiency, my tank doesn't have many fish and the snails eat any excess food, plus I do 50% water changes every 2 weeks, could this be affecting it?

shellby wrote: ↑Thu Apr 21, 2022 5:58 am I've got a Java fern with these weird black spots on the top of its leaves, and honestly, I'm stumped. Can anyone give me a clue what's causing this or how to stop it from happening?

I'd say it's not about how often you dose the iron, but rather that you're using it at all. With Flourish Comprehensive, you've already got sufficient iron in the mix. Java Ferns are slow growers, so they don't need a lot of nutrients or intense light. Too much of either can cause issues. That floating plant cover you've got is a great way to manage the light, but you've got to keep an eye on the fertilizers.

Your water changes do help, as they dilute the fertilizers, but you're adding them right back in again. I'd recommend doing a 50% water change every week - it's better for the fish and the plants, and it can help keep algae at bay.

Regarding micronutrients, Flourish Comprehensive has got you covered, but what's your GH level? And I'm still curious about the CO2 - is it diffused or something like Excel?