If your pool has accumulated what I can only guess to be calcium or other hard mineral deposits around the tile edging, you might know it's almost impossible to remove this scale. I have spent hours in the water with a pumice stone, rubbing until my hands were raw, even through a cloth 'protection.' No amount of scrubbing made any difference.
I saw advertised, bought and tried a 'miracle' gel which supposedly contained some type of acid which would cling to the crud and eventually detach it (I never was sure about what it would do to the water itself, but in short order I found it didn't work at all.)
I also tried pool acid itself... Muriatic. Diluted, then increasingly stronger. It works some, but you can't keep it where it needs to STAY due to that pesky gravity thing.
Then Terri brought home a one-sheet for a new process. One of the realtors in Lakeway had the detail... the process is called Soda Blast. Think of sand blasting or bead blasting but with Magnesium Sulfate. From Wikipedia: "Magnesium sulfate is a chemical compound containing magnesium and sulfate, with the formula MgSO4. In its hydrated form the pH is 6.0 (5.5 to 7.0). It is often encountered as the heptahydrate, MgSO4·7H2O, commonly called Epsom salt." Said to be softer than alternatives, and claimed to leave your tiles intact, and be PH neutral, we hired the guys.
They arrived in a big truck trailer with a VERY large compressor on the flat trailer. Hoses, pressure vessel, and mixture pumps were unloaded.
They lowered the water about 8 inches and drained the spa completely, then went to work blasting the tiles. The magnesium sulfate turns grey when wet, and so did the pool.
They 'sort of' cleaned the pool, but since so much of the stuff was in the water, obviously couldn't get it all.
I was told to refill, turn on the pumps and let them run for a while - 8 hours or so, then to backwash, and possibly repeat. After checking pressure on the filter, which surprisingly hadn't changed, I decided to let the pump run maybe 24 hours. The pressure still didn't change. Overnight the water went from really murky to clear!
You can decide for yourself if you think the process was successful. A good 4 years of crud is gone, the pool and spa look new and clean and, I am amazed.
The name of the company is Soda Blast Express.
Our water is sparkling clear today.