I don't think it will simply go away by itself, not without changing your water chemistry. From what I've read it is linked to low phosphate levels which you may have created by adding the additional plants to your tank. Here is someone's advice from the bcaquaria.com site;
Getting rid of Green spot algae
If your tank is experiencing green spot algae on plants, likely its due to low phosphates. If its on the glass but not on the plants, then just clean the glass, you are doing fine :P
Heres several ways to treat the problem.
Tank treatment, increase Phosphate dosing slightly in your EI fert regime.
Spot Treatment. Turn off filter, use a, b, or c. wait 5 minutes, turn on filter.
a) If you have your phosphate mixed into a solution, you can turn off your filter and dose your phosphates directly on the area thats affected.
b) If you have dry kh2p04, mix your EI dose with tank water just enough to make it dissolve. then pipette/syringe it onto affected area.
c) If you you do not have a phosphate solution, your alternative is Fleet Enema. use 0.3 ml of enema per 10 gallons. Do this daily until its gone since you have no fert regime. Water change every third day 50% to help keep the phosphates from getting out of control during this treatment.
For options a and b, if it keeps coming back on said area quickly, then you need to up the phosphates in your dosing regime. unless you are fine with spot treating the area every dose.
for option C, you run a risk of bottoming out on nitrates during the treatment sue to your lack of regular macro dosing. A high fish load counters this affect. If you have java ferns, this can cause them to blacken at the tips and melt a bit if the nitrates keep bottoming out. The plus side is the baffled look you get from the store clerk when you say, "no im not plugged up, its for my fish tank"