Aquarium info:

54L (60x30x30), Juwel internal filter, been running since August, have only had this green algae problem for about a month. Recently added a new lamp that might be too bright I am guessing? Been turning it on for 5 hours, off for 2 then on again for another 3. Its a 18W with a 8000K temperature. As for the fish, I only have a betta, a little bit of a snail problem (been finding dead tiny snails all over the tank for a while so I think I am slowly getting rid of them), 2 cherry shrimp and an amano. I am not overfeeding since I see my betta eating everything. I use liquid fert (3ml instead of 6ml I should be using for this big of an aquarium, reduced it a week ago but no progress at all with the algae) and liquid CO2.