They are like 4-500 for say a 20 gal res but I think we may see the market come down a bit as this tech is real mainstream now for the coral/plants/tropical fish and from the reading you may need a OPR (Oxidation Reduction Potential) meter... Because shock treatment will mess with your mag. and iron....ooh one more meter I need! But to treat incomming water...excllent
But if you are useing Rock Wool or have ever had pith or gnats... I would spend the $$$
FC