Dennerle do a similar kind of calcium product for shrimp, although I'm not sure how economical it works out. Off the top of my head, it's 5 drops per 20liters - I've been using 5 drops in my 20 liter ever week, and I would say I've used half a bottle in about 6 months. I use RO water and I've never noticed any pitting in the shells of my shrimp