I doubt the brand has anything to do with it though.
Are you:
-Mixing 2 tsp/
gal RO water
-Mixing well & settling for about an hour
-Dosing from a relatively airtight container
-Storing no more than a few weeks mixed at a time
I've heard you can mix vinegar in to increase the saturation level beyond 2 tsp/
gal, but I've never done it do can't really advise it.
It could be your tank has a higher demand than the lime can add; but your levels should be more steady than it was before
kalk ATO.