I have a 100litre (25g) cube with built in back filter. I use a HOG1 about 3 years now and the tank is barebottom with old live rock.Tank is skimmerless and the filter has activated carbon every month the HOG and extra pieces of live rock . I can't lower the phosphate enough (0,05-0,2) but the nitrate levels are always zero. Most of the time hair algae thrives in the tank rock, glass and pumps, at all levels in the tank, and in the HOG too, where I get thin strings of dark green algae. I tried to feed more(4-5 pinches of flake) with no results in nitrate level, but got a bit cloudy water every time and lost all my snails.There is a happy clownfish and a brittle starfish in the tank.I tried to bring nitrate up with KNO3 but it didn't accelerate the algae growth in the HOG. Tried to clean the rock manually to give advantage to the HOG but the hair algae returned as it was. Switched off the tank lights of periods of months( no corals) and kept feeding and nitrate level climbed up to 20ppm but the HOG didn't grow more algae. When i switched the lights on in the main tank the hair algae appeared again. I tried iron, manganese, and potassium to help algae in the HOG with no significant results.Ca, Mg, KH are fairly stable. Lights on the HOG are 24/7 most of the time but algae grows slower in the center.Should I cut some hours off?