I added a Tunze Kalk dispenser (5074.) It's mounted inside of my 7 gallon ATO bucket that hold my Osmolator pump and is is fed by a BRS top off pump. I dose Kalk overnight to support pH (pegs it at 8.20, controlled by the Apex)
I add Kalk the dispenser monthly and remove and clean it (5 minutes) about every 3 months. No moving parts exposed to Kalk, and the fail safes are pre-determined pump run times (based on uptake) and pH limit set in Apex outlet. Although it uses the ATO water supply, it functions independently of the ATO.
It's been in service about 6 months and has worked wonderfully so far.