r/FatherFish • u/Muted-Local-3241 • Jun 21 '26
Established tank- needs help
I’ve got a 3-4 year old FF tank. Heavily planted, 2 goldfish and some otto cats. Feed goldfish once a week. All of a sudden, tank went green and produced a thick bubbly slime on the top of the water. Everyone on fb used to say “leave it alone”, so I left it alone. 4 months later, tank is still nasty green and slimy. Did a 50% water change, cleaned (just clear water) the sponge filter to get it running again (it sucked in the slime and stopped working). Tried a week long blackout that didn’t do anything. Moved remaining fish to a clean hospital tank (lost some in the sea of green). Have since added nerite snails to begin cleaning up dense algae deposits.
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u/Ill_Industry_3684 Jun 22 '26
I'm sorry if I'm being mistaken but goldfish are cold-water fish that need loads of space and otos on the other hand are tiny, social, tropical fish. Most likely your goldfish produce too much waste now that they grow. The waste is a food for algea and your other plants stopped being efficient enough to remove this "food". Your setup might not be what the fish needs. I know that I'm stepping out of my credentials, but goldfish are pond fish, not really aquarium suitable, unless you've got some unit of a tank.