Will an empty tank stay cycled?

[talonbro]

So I've got this 20 gallon tank that's been running for months, but I had to move my fish out. If I leave it empty with just the filter running, will it stay cycled? Or is this a lost cause?

[stormyok]

It depends on how long it's empty. The bacteria need a food source, so if there's no ammonia, they'll start dying off. You could add a pinch of fish food every few days to keep them alive. Worked for me when I had to quarantine my Betta.

[leopard]

It depends on how long it's empty. The bacteria need a food source, so if there's no ammonia, they'll start dying off. You could add a pinch of fish food every few days to keep them alive. Worked for me when I had to quarantine my Betta.

Yep, this is the way. I'd also check your params weekly to be safe. If nitrites spike, you'll know the cycle's crashing.

[Oceanix9]

I've kept a tank cycled for weeks by dosing pure ammonia. It's more precise than fish food, but you gotta be careful with the amount. Like, a drop or two in a 20 gallon is plenty.

[Kairos9]

How long are you planning to leave it empty? If it's just a week or two, the bacteria might hang on, but longer than that and you're risking a full restart. I'd second the ammonia dosing if you're gonna be awhile.

[talonbro]

Thanks, everyone. Gonna try the fish food method since I've got some lying around. Appreciate the tips.

[carla_s]

Just don't overdo the food, or you'll end up with a nasty mess. Been there, done that. Took forever to clean the gunk out of my substrate.

[velvet8]

My LFS guy told me to use a raw shrimp if I was gonna be gone a while. Let it rot in there, then pull it out. Sketchy, but it worked.

[novakid]

shrimp method sounds wild but lowkey makes sense. bacteria gotta eat something, right?

[starlord]

My LFS guy told me to use a raw shrimp if I was gonna be gone a while. Let it rot in there, then pull it out. Sketchy, but it worked.

That's… creative. I'd worry about the smell, though. Ammonia dosing seems cleaner.