Brown algae spreading on fish tank

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Registered Member
Aug 22, 2021
I’ve had this fishtank for a few months (20 gallon with 5 GloFish Tetras and 3 Neon Tetras) brown has been growing on it and we did a water change cleaning the glass but it came back, can someone explain what this is and how to remove it? I wanna get rid of it before it harms my fish


AC Members
Jun 28, 2006
SF Bay area, CA
Welcome to AC!

Well, I have to say it doesn't look very bad in your pics to me. I know it's distressing to see but some diatom algae is normal for newer tanks. It can go away all by itself. No need to panic.

How long are your lights on each day? More than 6 or 8 hours is asking for trouble. I use a timer set so the lights are on when I'm able to see my tanks. You can also split the time, say 2 hours at breakfast & 4-5 hours later when you're home again.

1 other thing to think about is a dark background. It looks like maybe you get some bright lighting from behind the tank. It doesn't have to be direct window light to add too much light & cause issues. Try to think about where & how much light is going into the tank beside your tank lights.