I have a very similar setup... I have a 5 gallon de-rimmed aqueon bow (no cover) with the same planted + (12" one). I also had big problems with algae and constantly battle it which really sucks. I refuse to set up CO2 in an office tank this small...
Recently raised my light 6" above the tank and it seems to help out. The planted + is just too strong for a tank that shallow when you put it right on the rim (at least in my case...)
Inhabitants in mine are 1 betta and 1 otto.
I am assuming you do not use CO2?
Do you dose with anything?
Hopefully we can help each other out lol