According to
Wikipedia "For shock chlorination of wells or water systems, a 2% solution of household bleach is used", which tallies with Mark's recommendation. So I calculate that my 350 gallon tinaco requires 7 gallons of bleach. This is logistically difficult for me so I bought some solid "cloro" from Bellon instead. I thought this would contain 100% sodium hypochlorite but Wikipedia states that it might actually contain calcium hypochlorite and is also likely to contain less than 100% active ingredient (30% & 50% salts are mentioned).
Household Ajax cloro (Clorox) contains 5.25% sodium hypochlorite but I'm not clear on whether this is by volume or by weight. If I assume the latter (for simplicity), and also assume household bleach has the same specific gravity as water (I know it'll be slightly higher but don't think the difference will be significant), then:
7 gallons is equal to 26.5 liters
26.5 liters of bleach will weigh 26.5 kg (approx.)
26.5 kg bleach will contain 1.39 kg (~ 3 lb) sodium hypochlorite
My Bellon product seems to be used mainly for chlorination of swimming pools, so I assume it is actually HTH which "contains approximately 30% calcium hypochlorite". So does that mean I should add:
3x100/30 = 10 lb salt? Any chemists out there who can advise? I only bought 2 lbs as the guy being served previously said he added 1 lb per 18,000 gallons for pool chlorination, so thought only about 1/3 oz would be needed for my tinaco. Seems my alternate approach might not be so smart, so I might need to buy 14x 1/2 gallon bottles of Ajax instead to be sure of what I'm adding.