Who Gives A Fish Forums

My Anubias and Java Fern have been getting this weird slime coating lately. Tank is a 20 gallon, parameters are 0 ammonia, 0 nitrite, 10 nitrate. I do weekly 25% water changes and use a Fluval 207 canister filter. Lighting is on for 8 hours a day. Any ideas what's causing this?

That slime is usually biofilm, which happens when there's excess organic waste. How often do you feed your fish? Overfeeding can cause it. Also, check if your filter flow is strong enough to circulate the water properly.

Biofilm is harmless but ugly. If you wanna get rid of it, cut back on feeding and add some Amano shrimp or Nerite snails. They'll clean it up fast. Your tank sounds fine otherwise.

knightboy wrote: ↑Sat May 24, 2025 9:41 am Biofilm is harmless but ugly. If you wanna get rid of it, cut back on feeding and add some Amano shrimp or Nerite snails. They'll clean it up fast. Your tank sounds fine otherwise.

Yep, shrimp are a solid fix. I had the same issue in my 10 gallon, and a couple of Amanos cleared it up in a week. Just make sure your tank's cycled well for them.

Dude, I had this happen when I first started. Turns out my light was too weak, and the plants weren't using up the nutrients. Maybe bump your light up to 10 hours or get a stronger one? Just a thought.

Is the slime green or clear? Green could be algae, clear is probably biofilm. Either way, reducing light might help.

Thanks for the advice, everyone. I'll try cutting back on food and maybe add some shrimp. The slime is clear, so it's likely biofilm like you said.

tripleact wrote: ↑Sat May 24, 2025 12:40 pm Thanks for the advice, everyone. I'll try cutting back on food and maybe add some shrimp. The slime is clear, so it's likely biofilm like you said.

Good call. Let us know how it goes. If the shrimp don't do the trick, you might need to look at your filter media. Sometimes gunk builds up in there and causes issues.

Yeah, filter maintenance is key. I clean mine every month, but don't go overboard or you'll crash the cycle. Just rinse the media in tank water during water changes.

Also, if you're using liquid ferts, cut back a bit. Excess nutrients can feed the biofilm. I dialed mine back and saw a big difference.