Over the last few years I have had a problem with my spa water & plumbing having a calcium build up, calcium deposits & a flakey white mold. My local provider had me jump through all kinds of hoops trying this product & that with costs of $15 to $25 per product. Became more proactive, opened up the heater housing & found all kinds of build up that the spa pre-drain cleaners wouldn't touch. Manually cleaned the bulk out. My usual stain/scale control was part of the sanitizer so no real help THEN I found this product, which the locals said was no longer made, & add once a week. Water was clear before but now slightly cloudy which makes me think it is cleaning the plumbing which is what I want. Please note my local sources never advised to use the pre-cleaners prior to a fresh refill until the water was incorrigible after 15 years so now I also will use the appropriate additive before each refill. Next spring I will open the heater housing to see what kind of build up exists if any.