[Deanna]

Test your ammonia, nitrites and nitrates and let us know the results. How old is the tank? Am I right to assume that you aren't injecting CO2?

Air bubblers don't add oxygen. To get good gas exchange, you need to create strong rippling of the water's surface, but without breaking the surface. Your filter may be enough, but you also may need a small pump, like a Koralia, pointed up toward the surface.

Do a 30-50% water change.

 

[Deanna]

I'm not injecting CO2 right now. Should I? I have a CO2 system waiting to be added to the tank.

Well ...that's a whole other subject. If you want real good plant growth and the ability to grow a wider variety (more finnicky) plants, yes: CO2 injection is the way to do it. There are low-tech setups (no CO2 injection) and high-tech setups (CO2 injection). With high-tech setups, you also usually add quite a bit of light and need to fertilize at higher rates. Because the plants grow so much faster with CO2, you will also have to trim them weekly. In general, there is more maintenance and involvement with high-tech. It's not as much of a casual approach in the way that low-tech setups can be.

If you decide to do it, you can get all sorts of advice here on the forum. I'd also recommend this excellent guide that is sponsired by TPT: Planted Tank Guide. Make sure you get a good understanding of what a high-tech setup is before you plug the CO2 in.

Personally, I like high-tech now, but I also ran low-tech for many decades and was perfectly satisfied.