Who Gives A Fish Forums

Just got a new sponge filter for my 20-gallon tank. Should I seed it with media from my old filter, or is there a better way to cycle it faster? I'm worried about crashing my cycle if I move too much media.

Seeding with old media is the way to go. I'd take about a third of the media from your established filter and squeeze it into the new sponge. That'll kickstart the bacteria without destabilizing your current setup. Just keep an eye on ammonia for a few days.

Agreed with timber. I've done this with my 40-gallon and it worked like a charm. Also, if you have any floating plants, they'll help absorb excess nutrients during the transition. What's your current stocking like?

Yeah, squeezing the gunk from the old filter into the new one is legit. I did that with my betta tank and it cycled in like, a week. Just don't go overboard or you'll mess with the balance.

If you're worried about crashing the cycle, you could also run both filters side by side for a week or two. That way, the new sponge gets colonized gradually without stressing the system.

I've heard mixed things about using bottled bacteria. Some say it's a scam, others swear by it. Has anyone here had success with products like Seachem Stability?

dreamwave wrote: ↑Sun Jun 29, 2025 9:19 am I've heard mixed things about using bottled bacteria. Some say it's a scam, others swear by it. Has anyone here had success with products like Seachem Stability?

I've used Stability in a pinch, and it's okay, but nothing beats actual seeded media. Bottled stuff is hit or miss, kinda sketchy if you ask me.

I'm new to this, but why not just leave the new sponge in the tank for a while before turning it on? Wouldn't that let bacteria grow on it naturally?

Thanks for the advice, everyone. I'll try seeding with some old media and monitor the params closely. Appreciate the help!

softbreeze wrote: ↑Sun Jun 29, 2025 10:48 am I'm new to this, but why not just leave the new sponge in the tank for a while before turning it on? Wouldn't that let bacteria grow on it naturally?

That's a decent idea, but it'll take way longer without water flow. Bacteria need oxygen and nutrients to multiply, so a stagnant sponge won't colonize as quickly.