When I first set up my used tank, which had gunk and coralline skeletons and gunk covering 3 of 4 acrylic side panels and the overflow interiors, I filled my system (total volume about 200 gallons water) with fresh water and let all pumps run continuously for my leak test. I poured 3 gallons of vinegar in to clean the gunk and the new PVC I plumbed. After 24 hours, everything (coralline included) sloughed off easily with a scraper.