My pool is 6 yrs old, ~16,000 gal, white plaster. When we had it installed we went for the SWG. No problems whatsoever the first 2 seasons. CYA 0 and fc between .5-1.5ppm. Got black algae bloom season 3 (pool was 2 yrs. old). Put 5lbs of 99% diclor and brushed like crazy, and it went away...