I too would be weary of application in a display tank with lots of coral, though a lot of people report success with direct application via a medicine dropper. I think if you get your PO4
in control, it will go a long way towards inhibiting the algae growth you are experiencing. I go a month or more between water changes but I feed light and I run GFO
to keep PO4
as close to 0 as I can, and while I do have some algae in the tank, it is very much under control and not a nuisance. Occasionally, if I get a spot that is trouble, I'll just scrub it off with a tooth brush in the tank and do some manual removal. But I rarely do this. Once the PO4
is under control, a little clean up crew addition may bring everything where you want it.
It sounds to me like you may be over feeding, depending on what you have in the tank. I feed Rods Reef, and for a tank with several fish, I feed a small piece smaller than my pinky nail daily or sometimes even every other day.