Number one cause of Algae is excess nutrients in your system. For example high NitrAtes and any reading of Phosphates. Manual removal of the hair algae is a good place to begin. Method: Pinch the algae off the rock hold it in your fingers and remove it completely from the tank. Repeat. On a 300g reef a refugium should be at least 30g with LOTS of macro algae. Cheato and or other types will help reduce excess nutrients in your water.
unit is a must to help reduce nutrients at the source. If you own a unit it may be a good idea to change your filters out. Also if you are feeding multiple times a day reduce your feeding and the amount of food. If you are feeding frozen foods you will want to rinse them off in RO
water prior to feeding this will futher reduce excess nutrients bieng introduced to the tank. Flake and some pellet foods are already high in excess nutrients and can lend to algae issues.
Increasing the size of your refugium and or purning the plants in it as well as increased PWCs will help (provided your source water is at 0 TDS
) turn the situation around.