Thats what my next guess would of been....I am using the lucas formula as well....but prefer not to use that method.......of not changing the res......better to be safe than sorry....ya knowwell i figure since i havent changed res maybe they used it all up... so i cleaned old solution out its just straight ro water for a few hours and then im gona put lucas prozyme and a very very light mag cal solution in it. if that doesnt help ill up the dose...