I'm using the R0013 test from the Taylor kit where you fill up the vile until you can't see the black dot. Pool is crystal clear, just surprised it dropped. We did get a LOT of snow this winter, so maybe it did dilute. I just tested the water this morning and I have FC of 7, CC of 1, and I got the CYA back up between 30-40--since the test is kinda a guestimate. I guess whatever ate my CYA is dead, or it just diluted it from all the snow.