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I've been dealing with random ammonia spikes in my 55 gallon planted tank. Water params are good, 0 ammonia, 0 nitrite, 10 nitrate, but every few days ammonia jumps to 0.5 ppm. Tank's been running for 8 months, stocked with 10 neon tetras, 6 corydoras, and a pair of angelfish. Filter is a Fluval 307, weekly 30% water changes. Any ideas what's causing this?

That's weird, especially since your tank's mature. Have you checked for dead spots in the substrate? Sometimes debris gets trapped and rots, causing ammonia spikes. Also, how often do you clean the filter? Overcleaning can mess with the bacteria colony.

Yo, I had this same issue last year. Turned out my filter media was clogged with gunk, so the flow was weak. Check if your Fluval's output is strong enough. Also, maybe cut back on feeding for a bit, see if that helps.

turbokid wrote: ↑Mon Jun 23, 2025 2:10 am Yo, I had this same issue last year. Turned out my filter media was clogged with gunk, so the flow was weak. Check if your Fluval's output is strong enough. Also, maybe cut back on feeding for a bit, see if that helps.

Flow issues make sense. But OP, have you added any new fish or plants recently? Sometimes hitchhikers die off and cause spikes.

I'd test your tap water too. Some municipalities add chloramines, which can break down into ammonia. If that's the case, you'll need a better water conditioner like Seachem Prime.

Ngl, this sounds sketchy. My buddy's tank did the same thing, and it was a dead snail hidden under the driftwood. You got any inverts in there?

Thanks for the suggestions, everyone. I'll check the filter flow and substrate tonight. No new additions lately, and I use Prime already. Didn't think about a dead snail though—I do have a few nerites.

mythiclad wrote: ↑Mon Jun 23, 2025 4:20 am Thanks for the suggestions, everyone. I'll check the filter flow and substrate tonight. No new additions lately, and I use Prime already. Didn't think about a dead snail though—I do have a few nerites.

Keep us posted. If it's not the snails, maybe try a deep vacuum of the substrate. Sometimes it's the little things we overlook.

For real, substrate gunk is sneaky. I started using a turkey baster to spot-clean my sand, and it made a huge difference. Also, how's your bio-load? Those angelfish might be outgrowing the tank.

Bio-load could be a factor. Angelfish are messy eaters. Maybe try feeding smaller portions twice a day instead of one big meal. Less waste that way.