Who Gives A Fish Forums

I've been running CO2 in my 20 gallon planted tank for about a month now. My drop checker is lime green, but my fish seem a bit sluggish. Is 30 ppm too high for them? I've got Neon Tetras, a Betta, and some Cherry Shrimp in there.

30 ppm is usually fine, but Bettas can be sensitive. What's your pH and KH? If those are outta whack, it could mess with how the CO2 affects the fish. Also, how long are you running the CO2 each day?

I agree with willy. My Betta didn't like high CO2 either. Maybe cut it back to 20 ppm and see if they perk up. Shrimp are usually chill with it, but Tetras can be sketchy.

willy wrote: ↑Thu Oct 09, 2025 2:53 pm 30 ppm is usually fine, but Bettas can be sensitive. What's your pH and KH? If those are outta whack, it could mess with how the CO2 affects the fish. Also, how long are you running the CO2 each day?

pH is around 6.8, KH is 4. CO2 runs for 6 hours, starting an hour before lights on.

That KH is low, so your CO2 might be hitting harder than you think. Try bumping the KH up to 6 with some crushed coral or baking soda. Also, maybe shorten the CO2 period to 5 hours and see if that helps.

Yep, low KH can make CO2 more unpredictable. I'd go with willy's advice. My tank was similar, and adjusting KH made a big difference. Fish were way more active after.

Thanks, gonna try the crushed coral and shorter CO2 period. Appreciate the help!

No prob. Let us know how it goes. Sometimes it's just trial and error with this stuff.

willy wrote: ↑Fri Oct 24, 2025 3:11 am No prob. Let us know how it goes. Sometimes it's just trial and error with this stuff.

Exactly. Took me a few tries to get my CO2 dialed in too. Patience is key.