Liquid Carbon Products
Seachem Excel, API CO2 Booster — contain glutaraldehyde. Dose daily, boosts plant metabolism.
Not true CO2 — plants can use but effect is limited. Kills certain algae (BBA, staghorn). Vallisneria is sensitive to it.
Yeast CO2 System
Sugar + yeast + water in bottle connected to diffuser = slow CO2 release. DIY cost: under 10 USD.
Pros: cheap, simple, real CO2. Cons: unstable output, needs weekly refill, temperature-sensitive.
Night Aeration Off
Run aerator only during lights-off period. During lights-on, plants consume CO2 from water without it being driven off.
Cheapest option — zero cost. Only benefits heavily planted tanks with enough fish to produce CO2.
When to Go Pressurized
If you want true high-tech growth (red plants, carpets, fast stems), pressurized CO2 is worth the 150-300 USD investment.
Most low-tech tanks don't need it. Focus on lighting and ferts first.