Cookie. Since I have 1,000 gallon stainless steel milk tank, it looks like about 1 oz at first, then 1/4 oz per week. Does that sound right?
The tank is covered so might not have chlorine burn off like swimming pools do ...wonder if that makes a difference?
(The site said this) DRY CHLORINE - also called calcium hypochlorite has the added benefit of extended shelf life. Providing it is kept dry, cool and in an airtight container, it may be stored up to 10 years with minimal degradation. If one is wanting to keep chlorine in larger quantities, this is the item to store as it is readily available at swimming pool supply stores and many hardware and grocery stores carrying pool items and requires less actual storing space than its liquid counterpart.
For chlorinating water in rain tanks, Western Australia Health Dept. regulations state for first time chlorination, add 7 grams dry (1/4 ounce by weight) or 40ml (1.35 ounces) liquid per 1000 liters (264 gallons) and let stand for 24 hours before drinking. To maintain adequate chlorination, on a weekly basis add 1 gram dry (.035 ounce by weight) or 4ml (.135 ounces) liquid per 1000 liters (264 gallons) of water. Let stand for two hours before drinking."