How to drop Alkalinity and keep it stable?

[RuGlu6]

Thanks for replies people,
Sorry forgot to mention the obviously needed info.
Cal level is 420ppm
Ph main tank 8.3-8.4
Ph Reactor effluent 6.6 with one bubble every 4-6 seconds, can't make it anything less the that.
Reactor effluent is steady drip but fast enough to not to be able to count drops.
I just switched to Reefers Best salt maybe this will make it better...
I have few SPS and some LPS so there is a need at least for some Calcium.