Urchins are GREAT algae eaters IMO. U could probably get a red or blue tuxedo urchin. They stay pretty small. I have three in my 180 and they keep the rocks pretty clean.
http://www.liveaquaria.com/product/prod_display.cfm?c=497+530+2911&pcatid=2911
I caught it and moved but when i checked on him this morning, he was dead. :waa::waa::waa::waa: I had been feeding him a lot, including nori sheets, but he was still getting thinner.
That same thing happened when i got a watanabe angelfish. My powder brown bullied it for a day, but he stopped bullying it after. A 75 gallon is a little small for a 5-6 inch powder brown though.
IMO I would try an urchin. They are really efficient algae eaters and some can be very colorful :)
http://www.liveaquaria.com/product/prod_display.cfm?c=497+530+2911&pcatid=2911