How to drop Alkalinity and keep it stable?

[RuGlu6]

Hi guys,
My Alkalinity is 15, a bit too high. (30 drops with elos test to get water from clear to blue to yellow)
I have tiny calc reactor (Acro-Cal) and running 1 (one) Co2 bubble every 4-6 seconds in a bubble counter, can not make it any less then that with needle valve from J&L.
Increasing the flow through the reactor doesn’t seem to help with Alk drop, but only in Ph increase in the effluent.

Any ideas on how to drop Alkalinity and keep it there stable?
thx