Why are my aquarium plants turning black and dying?

Aquarium plants turning black? Yeah, that can definitely happen.

In most cases, this is a type of black beard algae that stays pretty small and forms tiny black spots. After a while, the whole leaf is covered in these black dots, and then it looks like your aquarium plants have black leaves. Run your finger over the dark area and you’ll notice it feels rough, kind of like a beard. In this article, I’ll explain how to fix this problem. Also, check out my guides on aquarium plants turning yellow, brown, or transparent!

Why are my aquarium plants black?

Well, like I said, it’s usually a type of black beard algae. And this algae shows up because of a few things:

• A lack of CO2: you’re just not adding enough (or any) CO2
• Unstable CO2: too little CO2, then too much, then cutting it back again …
• Poor water flow, which means not enough CO2 spreads around
• …

I really recommend reading my detailed strategy to fight black beard algae, it’ll definitely help you. But here are a few quick steps that already make a big difference in battling this annoying algae and preventing your aquarium plants from getting black spots.

How to fix aquarium plants going black?

You’ve got a few ways to do this:

1. Add more CO2. Install a CO2 system if you don’t have one yet (seriously, it’s the best investment for any planted tank!) and slowly increase the CO2 week by week. Meanwhile, trim off the affected leaves and healthier growth will come back.
2. Once you’re adding CO2: keep it as stable as possible! Start injecting CO2 about an hour before your lights switch on so it’s well mixed by the time your plants need it. And don’t mess with your CO2 settings too often—max once a week, and only in small tweaks.
3. Dim your lights. More light means faster plant growth, and that creates a higher demand for aquarium plant fertilizer. Chances are you’ve created such high demand that your tank can’t keep up. Result: CO2 shortage and aquarium plants getting black spots! By lowering the light, you reverse that process.
4. A combo of more CO2 and less light is super effective. Highly recommended 🙂

What if you don’t have a CO2 system?

No budget for a CO2 system? You can use a liquid carbon source instead—this algae doesn’t like that either. But honestly, I still believe a proper aquarium CO2 kit is a must-have for every planted tank and hands down the best investment you can make for healthy plants.

PS: you’ll need to trim off the leaves that are already too badly affected, since the black won’t just disappear on its own.