First thing first, you must ID the algae that is causing the problem because the treatment is very different.
Like for dinoflagellates, raising the PH to 8.4 or 8.5 solved my problem 100%. I found getting rid of dino the easiest thing I have ever done in my aquarium. I used Seachem OH balance to raise my PH slowly.
http://www.aquavitro.com/Products/balance.html
for cyanobacteria it is a bit more complicated and the nutriments in the water are too high.
As for if you have too many fish, if your nitrates rise fast even with water change than you have too many.
The best way to ID the algae is to use a small microscope that can do 200X or if possible 400X. At 200X you still can see them. That way it is very easy to ID dino, diatomes or cyano.
Second is to test your water for ammonia, nitrites and especialy nitrates and phosphates. Put some GFO (ferric oxide) in your filter (rinse it well). That will remove the phosphates.
Plus what is the source of your water? RO or tap? if you are using RO water check the TDS to make sure it is efficient. If you are using tap, stop using that as you might just fuel more the algae with every water change. Buy a RO unit.