Great tank, I love my
ADA mini L its a good size if you ask me.
How long is your light period, or how long do you shoot for? Definitely get a timer it will help with making adjustments. Just for a reference im running 24 watts (3 X 8 T5) on the same tank with pressurized CO2 and a 7.5 hour day lamp duration with a mid day blast.
I was getting some green hair algae at one point but i think it may of had to so something with the cheep Chinese bulbs that came with my light setup. Once i switched out to better quality ones and did a 3 day black out i went back to the same light timing and i still haven't had any issues.
Still i think you may be able to get away with the amount of watts you are running, you will just need to adjust how long they are and keep the CO levels up.