I know Randy has said the aquarium brands may be purer than the lime you buy at a grocery store, but I've been using it for at least a year with no issues. Kind of hard to mix it wrong too. You can use it at full saturation (about 2 tsp per gallon), so you really can't add too much lime to the water. Of course, like jumpincactus said, you can add to much of the limewater solution to your tank (has to be dripped slowly), so keep an eye on your PH. I did recently read a post about some potential nasty stuff in the precipitate, though, so whatever dosing method you use, be sure not to get the white stuff left on the bottom. Also, make very sure you're getting "pickling lime" and not pickling salts or pickling spices or pickling anything else.