[Myka]

150 mL of high capacity GFO for an 80-gallon tank is too much for a first dose imo. I would try a third of that at first. Stripping a tank of phosphate really fast is a really bad thing - especially if the phosphate has been high for a long time.

From Get Rid of Hair Algae & other Nuisance Algae in my signature (referring to normal capacity GFO): We're gonna be safe and assume there is a lot of phosphate in your water, so add about 1 mL GFO per gallon of water in your reef. In 3 weeks add another 1 mL/gal to the existing media. In another 3 weeks (6 weeks total) dispose of all the old media. Refill with 2 mL of fresh GFO per gallon and let it run for 6 weeks. Dispose of old GFO and refill with 3 mL GFO per gallon and let that run for 6 weeks. Usually 3 mL GFO per gallon is a good maintenance amount, but some people use significantly more or significantly less. You will learn when you have to change it out because you will start to see some algae growing usually on the front glass is the first sign, and adjust the amount of GFO you use so that you can change it every 4-6 weeks.