I don't think its the wattage that's your problem nor the w/c weekly.
How much are you doing like 20-30% w/c? That's sufficient enough.
What I'd do after what I now learned with my hardcore algae attach if this was my tank: Use a dish sponge/ scrubby pad and clean your tank sides out, then while there's all that stuff "floating" do your w/c (maybe need a lil more then normal).
Then set your lights to something like 4 on 4off 4 on or 5-4-5 something that gives a light break in the PM for about 3-4hrs.
Then see to get Excel again and start dosing as recommended on the pack for 10g.
Within 1-2 weeks you should then see the matter becoming much better if not fully disappear. Make sure meanwhile your NO2, 3, Ammonia is not gonna go up for no reason to feed the algae even more.
All that will conquer the green algae issue at least - Now what that "white stuff" is you were talking about I still don't know, any way you could take a picture of it for me???