Lighting Question 20 gallon long

[llama0788]

20 gallon long
30x13x13 (inches)
2 medium size patches of dwarf hair grass and a large fully grown amazon sword plant

I bought it used with a 96W Power Compact lighting system (getting rid of this is not really an option at the moment). I have been having some problems recently with hair algae so I was wondering how long of a photo period I should have the lights on for.

Thanks!

 

[Rhino]

I do 7 hours in my tank.