Seapool? Nope - C-Pool!

[waterbear]

If you want to "mix your own" the 4th page of the patent description gives the formula!

All you need (for every 10k gallons of water) is:
10 oz. of "bluestone" (copper sulfate pentahydrate)
1.5 lbs alum (used as floc in pools for years!)
2 oz. of salt (according to the patent, sodium chloride is a chlorine source because it supplies Cl- ions! Scary! )
1 lb soda (Arm and Hammer Super Washing Soda or some pH up)

(Kids, don't try this at home!)