Who Gives A Fish Forums

Noticed a weird slimy film on the surface of my 75 gallon Discus tank. Water params are good, 0 ammonia, 0 nitrite, 10 nitrate. Running a Fluval FX6, temp at 84F, weekly 50% water changes. Anyone else deal with this? It's kinda sketchy.

Biofilm can pop up if there's too much organic waste or low surface agitation. What's your feeding routine? Overfeeding might be the culprit. Also, check if your filter outflow is strong enough to break the surface tension.

I had the same issue in my 100 gallon. Added an air stone near the filter return, and it cleared up in a few days. Are you using any surface skimmers? They help a ton with this.

Magpie wrote: ↑Thu Jun 05, 2025 3:01 am Biofilm can pop up if there's too much organic waste or low surface agitation. What's your feeding routine? Overfeeding might be the culprit. Also, check if your filter outflow is strong enough to break the surface tension.

Yep, overfeeding's a common trigger. I cut back to twice a day with smaller portions, and the film vanished. What's your substrate? Detritus buildup can contribute too.

My tank's got a similar setup, 75 gallons with sand substrate. No biofilm though. Maybe check your filter media? Could be clogged and not moving enough water.

This happened to me last month! I freaked out, but it's usually harmless. Just increase surface movement like Vista said. Also, how old's your filter? A good rinse might help.

Never had biofilm, but my tank's heavily planted. Maybe add some floaters? They soak up excess nutrients and reduce surface scum.

Thanks for the tips, everyone. Gonna try the air stone and cut back feeding. Appreciate the help!

PureAddict wrote: ↑Thu Jun 05, 2025 8:05 am Thanks for the tips, everyone. Gonna try the air stone and cut back feeding. Appreciate the help!

Let us know how it goes. If it persists, test for phosphates. Sometimes they're the hidden culprit.

Oh, and if you're using any oils or supplements, they can cause film too. Double-check your water conditioner.