The regular prizm they say is rated for tanks up to about 100 gallons, and the prizm pro is rated for tanks up to 300 gallons. Most people recommend that you cut those numbers in half, and thats what they are really good for. I have both models the prizm, and the pro. They work O.K., but I think they require to much fine tunning, and maintenance. I have a seaclone, and berlin, and I never have to mess with adjustments on them.