What is your pH? What measure are you using for alk? (dKH or meq/l) Please list your parameters. Salinity, pH, Alk and Ca. You should be around 2.8 - 3.5 meq/l, pH 7.8 - 8.2, Salinity 1.023-1.025, Ca 380 - 450. Also I have seen some comments relating to purple up possibly causing problems. Also try this chemistry link /url
http://home.comcast.net/~jdieck1/chem_calc3.html /url
Doug