I use Seachem Prime (it's the specific product). It's a little more expensive, but it's concentration is about five times as much, so drop for drop, it's much more cost effective. You really shouldn't be able to overdose on products that remove chlorine and chloramines, unless you're really just pouring it in like crazy. If you remove 50% of the water in a partial water change, you're supposed to dose for the full volume of the tank according to the instructions. I generally dose for 80% of the tank if I am removing 50% of the water. You can add the product straight to the tank if adding it to the water before adding it is not possible.