Hi Javier!

Algae is a consequence of nutrient (ammonia, nitrate and phosphate), sunlight and temperature. Your water is warming up, your fish (bigger now!) are waking up and the sun is shining longer. Right now, the string algae is your friend. It is sucking up some of the ammonia that your fish are generating and providing a little spring "salad" for them to nibble on as they wake up. Leave it be. As things warm up, your biofilter should reduce the available nutrients in the water and the algae growth will slow down. Hair algae and "pea soup" algae are independent problems but have the same causes. The microscopic algae can be controlled with UV, the hair algae cannot.

Smart control of algae depends on reduction of nutrients and control of solar exposure. Algaecides pollute; most string algae "fixes" don't fix.

Bob