As far as PO4 test kits go, is there an advantage to using one of these in favor of the other? Is one better, or easier, or more accurate? The Salifert is a few dollars more, not much though. Seachem $9 to $10 US; Salifert $16 to $17 US. I use AP and Seachem for NO3. They seem to work fine and give me the same reading. I've not yet tried any Salifert kits. I'd like to try to avoid the outlay for Hach or LaMotte, but can if need to.