CO2 Items
CO2 is the single biggest lever in a planted tank, and also the one most likely to kill fish when it goes wrong. Here is how to think about it before you buy.
Do you actually need it?
Not always. Anubias, Java fern, Bucephalandra, Cryptocoryne, mosses and most easy stems will grow well without injected CO2 — slower, but healthy, and with far less algae risk. You need CO2 when you want a dense carpet, strong red coloration, or the compact, tight growth you see in competition scapes. Adding high light without adding CO2 is the most reliable way to get an algae problem: the plants cannot use the light, and algae can.
What a complete system is
A CO2 setup is a cylinder, a regulator with a needle valve and solenoid, a bubble counter, tubing rated for CO2, a check valve, and a diffuser or inline atomizer. The check valve is not optional — without one, tank water can siphon back into your regulator overnight and destroy it. Put the solenoid on the same timer as your lights so gas is off while the plants are not using it.
A drop checker is the one piece people skip and should not. It is the only way to read your dissolved CO2 rather than guess from bubble count, and bubble count means nothing across different tanks.
Dial it in slowly
Start low and raise the rate over days, not minutes. Watch the fish, not the drop checker, for the first week — fish gasping at the surface in the afternoon means CO2 is too high, and the concentration climbs all day while the gas is on, so a rate that looked fine in the morning can be dangerous by evening. Increase surface agitation if you need a safety margin. It off-gasses some CO2, and it is a cheap insurance policy against a stuck needle valve.
Come talk a setup through with us before you buy the pieces — a CO2 system is easy to assemble into something that does not quite work together.