I have been slowly upgrading my test kits from the basic API color charts. I must be a little color blind. Can never read those color differences. I recommend the aqua forest for Mag and Alk. They change color at the reading point. My question, looking for personal experience. Is the Hanna checker a good investment for phosphate or does anyone use something else? How cost effective are the Hanna's? Once u have the checker u just need the refills after that correct? How many test do you get per reagent refill?