Who Gives A Fish Forums

I set up a CO2 system last week for my planted tank, but my tetras seem stressed. They're gasping at the surface more than usual. My drop checker is green, but I'm not sure if it's accurate. Could the CO2 be too high?

What's your bubble count per second? If it's cranked up too high, even a green drop checker might not save your fish. Gonna need more deets, like tank size and how long the CO2 runs daily.

Surface gasping is a red flag. Check your pH and KH to calculate dissolved CO2 levels. A green drop checker is a rough guide, but it's not foolproof. Also, are you running an airstone at night? Plants stop photosynthesizing then, so CO2 can build up.

Yep, agree with deepsea1. My bettas did the same thing when I first added CO2. Had to dial it way back and add more surface agitation. Now they're chill. Maybe try lowering the bubbles and see if they perk up?

My tank's 20 gallons, and I keep the CO2 at 1 bubble per second. Fish seem fine, but I also have a sponge filter for extra oxygen. Maybe your filter isn't agitating the surface enough?

Had a similar scare last month. Turns out my drop checker fluid was expired. Swapped it out, and boom, problem solved. Worth checking if yours is fresh.

How's your water flow? If it's too stagnant, CO2 can pool in certain spots. My canister filter keeps things moving, so the gas distributes evenly. Tetras are sensitive, so they'll show stress first.

SunnyG wrote: ↑Tue Jul 22, 2025 6:49 am Had a similar scare last month. Turns out my drop checker fluid was expired. Swapped it out, and boom, problem solved. Worth checking if yours is fresh.

Good point. Also, test your water for ammonia. High CO2 can lower pH, which might spike ammonia if your cycle's not rock solid.

If your fish are gasping, cut the CO2 immediately. No debate. Then slowly reintroduce it at a lower rate. Better to lose some plant growth than your whole school.

Thanks, everyone. I'll lower the bubbles and check the drop checker fluid. Appreciate the help!