Liter meter, check it out. It's expensive but i have read all good things, it's setup so you purchase the base unit, like a reef keeper, then add the modules or attachments. Like the auto water change/ top off kit. Comes out to be somewhere in the 400$ range but all the folks I know that use it like it. They say their corals love it!! My plan was to purchase one in feb and use it to do a few gallon change daily, then do a 20% change bi monthly. Just to be safe. My corals
Love water changes!! They told me so!! Lol jk