I keep reading that co2 keeps algae under control. My tanks do not have any injected co2.But, they to receive liquid co2 once when I do a water change and another 3-5 days before another change usually 7-10 days.
Same thing here with hair algae in 1 of my tanks. Strangley this is one that actually has a CO2 feed. I'm cutting it off right now with aquascape scissors but next time I cut back the grass I'll drop the water level and trry to scrub it off the plants and hardscape.
In my experience CO2 does not prevent algae. i use passive CO2 and have had algae issues and traced the issue to the fertilizer. Algae (Especially Hair and hard green spot algae) is typically an indication of a nutreint problem in the water.
Once a week, after a 50%water change (RO water TDS1ppm), I dose micro nutrients to the following levels:
Iron 0.1ppm (FeDTPA)
Manganese 0.05ppm (MoEDTA)
Boron 0.02ppm (Boric acid)
Zinc 0.02pppm (ZnEDTA)
Copper 0.01ppm (Cu EDTA)
Molybdenum 0.005ppm (NaMO3)
nickel 0.005ppm (NISO4) only nutrient that must be dosed daily.
I increase GH to a minimum of 1 degree GH (3parts Ca and 1 part Mg
And other macros to:
Phosphate 1ppm (KHPH4)
nitrate5ppm (currently experimenting with 15ppm (KNO3).
Potassium, Sulfur, and Chlorine (yes it is a plant nutrient) are not tightly controlled but are well above needed. Sulfur and Chlorine typically come from my GH booster.I use a decorative snail shell for pH control PH. PHis typically between 6.5 and 7.2.
The only algae I have in my tank right now is green slim on the glass (I use snails s to control it. For my 5 gallon one or two Nerite snails are enough to keep the glass clear I use RO water with a TDS of 1ppm). i also have passive CO2 to insure I have enough (it cannot be detected PH or drop checker). It is a shrimp tank and I have not had any problems with shrimp even at Copper levels 3 times higher than listed above. Tank is currently being reset.
Note Most fertilizers on the market depend on your water supplying some nutrients. I tried 4 commercial different fertilizers without success in this tank with no consistent plant growth due to my water and inert substrate. So after years of trying I made my own fertilizer. Just using a fertilizer is no guarantee that you will have all nutrients at a sufficient level to avoid problem algae. And Even if you dose to my levels PH, KH, interactions may neutralize some of the ingredients in the fertilizer resulting in Algae.
I have experiemented with different light setups over the years and found it had no effect on algae.
I tried liquid CO2 in the past but saw no evidence it helped my plants and in fact it harmed some of them. And too much is definitely potentially harmful to the fish. In my opinion it is not worth it.