Oh, pejerrey, what are you trying to do? Actually help the guy fix the problem instead of putting a bandaid over it? LOL!
Generally speaking, when hair algae is involved, the root cause is almost always due to too much light.
You know, sooner or later somebody is going to ask all those questions or the OP is going to realize he needs to know the answers to know the cause.
Otherwise we will be playing a guessing game and giving him all kind of advices based on poor info. Frustration will be inevitable.
As you say, I agree that light vs co2 is the main thing. But does the op know why?
Even if one of us or all of us advice(s) him right and solves the problem, other things are going to happen in the future and he may not be able to troubleshoot it.
..."Give a man a fish and he will get a bowl, teach a man how to keep fish and he will get a planted tank"...
Dont take me serious I'm a clown!
The truth is that without enough co2 plants are limited to the nutrients they can consume in a tank, given more than enough light in relation to the available co2 then algae will happily process the nutrients that the plants can't process. This is also determined by the plant mass and any other limiting factor.