I'm trying to figure out which kit I need. What is the PO4 that we measure?Greg, I received your request today. First, are you looking for just the reactive phosphorus (orthophosphate) in your sample or the total (ortho & meta)? If you want total we need to look at a different kit. If you do want just ortho, the kit that you mentioned would work just fine. Accuvacs are used instead of sample cells and powder pillows. They are vacuum pressured ampoules that already contain the reagent in them. You submerge the ampoule in your sample breaking the glass tip and the ampoule fills with your sample due to the vacuum pressure. This is a very easy way to do your testing but ends up costing a little more per test. Please let me know if you have any further questions or if I can create a quote or place an order for you. Thanks!