I purchased a 200 gallon mix last week, I made 30 gallons up today for my water change tomorrow. I will test my PO4 before I do the water change to see what PO4 the ESV salt contains in my mixing bin.Started hobby in '05. Went from Tropic Marine Pro, Seachem, back to TMP, DD H2Ocean, RC and I am now with ESV. TMP was very good but the ALK was always way too low and it was very expensive. DD H2 was pretty good. My corals seem to love it but it left tons of brown calcareous deposits on my pumps and ceased them up. Same with RC. No deposits with ESV but I'm currently experiencing 0.14 PO4 with ESV (first 200g kit I've brought). I may purchase the 25 or 50g next time to see if I get the same PO4 levels. Mixing with scale can be a wee bit time consuming but it mixes clear in no time.