I would like to write about the Tunze Osmolator auto top off unit .This is by far the best unit I have used. It is very well built and easy to dial in. I bought mine used for about $125 (brand new $195)and I never had a problem with it . The optical sensor keeps my salinity right on and never have to worry about over filling into my sump. About once a month I do take the sensor off and give it a good vinegar soaking just in case The pump can be a little noisy at times but it does it's job. If the pump does happen to go out, a brand new replacement is only like $20. If I am not mistaken I believe Reefer Rob just purchased one and he loves his. Can't go wrong with anything tunze.