Ive been using the same Maxi1200 for a year now, no problems at all, what kind of kalk are you using? Mag pumps and Maxi jet pumps both work on the same principle, if the Maxi isnt working, I doubt the Mag will last much longer,,... Did you start with a NEW Maxi? Also, how long, total, are you mixin in a 24 hour period?