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So I just got home and my tank smells like rotten eggs. Water looks cloudy, fish are gasping at the surface. Did a 50% water change yesterday, params were fine. What's going on?

Rotten egg smell usually means hydrogen sulfide, which happens when substrate gets anaerobic. How deep is your sand bed? Also, check if your filter's flow is blocked.

Tangazo wrote: ↑Sun Jul 06, 2025 7:05 am So I just got home and my tank smells like rotten eggs. Water looks cloudy, fish are gasping at the surface. Did a 50% water change yesterday, params were fine. What's going on?

Yo, that's sketchy. Did you stir the substrate during the water change? Sometimes gunk gets trapped and releases toxins. Also, what's your filter media look like? Clogged filters can mess with oxygen levels.

Cloudy water plus gasping fish suggests a bacterial bloom consuming oxygen. Test for ammonia and nitrite immediately. If those are high, add an air stone and do another water change.

Oh no, poor fish! I'd do another water change ASAP, maybe 30%. And yeah, like zylux said, an air stone could help. Have you added anything new to the tank recently?

CalmEcho wrote: ↑Sun Jul 06, 2025 7:14 am Rotten egg smell usually means hydrogen sulfide, which happens when substrate gets anaerobic. How deep is your sand bed? Also, check if your filter's flow is blocked.

For real, that substrate can be sneaky. If it's deeper than 2 inches, you gotta stir it weekly or go bare bottom. Also, what kinda filter you running? Hang on back? Canister?

I had this happen once after overfeeding. The uneaten food rotted and caused a spike. How much are you feeding? Maybe cut it back for a few days.

Hydrogen sulfide is dangerous but dissipates quickly once exposed to oxygen. Stir the substrate gently, increase surface agitation, and monitor fish closely. If ammonia or nitrite are above 0.5 ppm, use Seachem Prime to detoxify.

Dude, that's a nightmare! I'd throw in some activated carbon to help clear the water. And yeah, like everyone's saying, check those params again. Sometimes stuff goes sideways fast.

The gasping indicates hypoxia. Ensure your filter outflow is creating surface movement. If not, adjust it or add an air pump temporarily.