Going to need a lot more info than this...
1.) What size tank do you have?
2.) What kind of lighting do you have? Duration?
3.) What kind of substrate are you using?
4.) How are you injecting co2? Pressurized or DiY?
5.) How are you monitoring your CO2 levels? What is the ppm?
6.) What is your water change schedule?
7.) What is your KH/GH/TDS?
8.) What do you have for fish or inverts?
Lastly, pictures are worth a thousand words!
What makes you think your CO2 is fine if you don't check it? I would check the ph of tank water that's been in a glass overnight, and then check again right when your lights come on. You want a ph drop of 1 full point.Well, I’m doing 2 bubbles a second. I don’t test co2 levels, Ige kept it at 2 bubbles per second for like 6 months but now I’m getting algae. It’s probably not the co2
I also dose flourish fertilizer.
What makes you think your CO2 is fine if you don't check it? I would check the ph of tank water that's been in a glass overnight, and then check again right when your lights come on. You want a ph drop of 1 full point.
What kind of Flourish are you dosing? Flourish Comprehensive? Comprehensive is anything but comprehensive; it doesn't contain any macronutrients. I would look into something like Thrive or EI dosing.
Finally turn off that second light, and reduce your photo period to 6 hours. That will help while you figure out the rest of it.
Jellopuddinpop asked you what kind of Flourish were you dosing because there is more than one. Light, 20W LED over 10 gallon is a lot of light. I would turn it to 50 - 60%. When you do a water change, what water do you use? What is its Ca, Mg, KH and TDS? You can get the info from the water works if you use tap water.
Why is there suddenly issues with algae, you ask? Because the plants used up their nutrient reserves.
You ordered Thrive fertilizer which I can’t help you with because I don’t know anything about it. We use mostly standard fertilizing minerals, like K2SO4, KNO3, KH2PO4, MgSO4 and CaSO4.
If you mean Flourish Comprehensive then there is almost nothing in it but iron Fe. It was meant to be used with Flourish Trace to have more complete trace element mix. These are micro nutrients. And because you have been adding only one micro element and no other micro and macro elements the plants used up their reserves and became weak. They couldn’t fight algae any longer.
That's a heavily planted tank man, you definitely need a good dosing regime. Once your plants start growing well, your issues should go away.
I always find it fascinating though, how some people get to grow lush tanks with little to no knowledge and some do their best for the plants and don't achieve success.
5. Well, I’m doing 2 bubbles a second. I don’t test co2 levels, Ige kept it at 2 bubbles per second for like 6 months but now I’m getting algae. It’s probably not the co2
2 BPS CO2 is probably no longer adequate for your increased plant mass...it may have been fine initially but I suspect your plants are now limited by a low amount of CO2. You should be getting a 1.0 pH drop...a pH pen like this can help
Once dialed in you'll probably find yourself limited by some other nutrient - N, P, K, etc. - but start with CO2
Lastly, IMO this is recommended reading for those with algae issues
I agree with almost everything said here, except that the pros use Excel to control their algae. While many people do dose liquid carbon, I would say their clean tanks come from intensive maintenance, and proper balance of light, ferts, and CO2. Liquid carbon may have a place, but I think most serious planted tank enthusiasts use it as one tool in a very large toolbox.Pros use Seachem Excel to prevent Algae especially hair algae.
You probably have too much light or other imbalances but instead of chasing fertilizer params, use a comprehensive like Thrive (its fine).
Keep up with substrate cleaning, maintenance, water changes and with Excel you should be rid of your algae in no time.
Lookup @Deanna algae bomb with Excel.