[tang daddy]

technically if your rx comes on at 6.7 and goes off at 8 then either you have 2 ph monitors or you have set it wrong!!

the ph set for your monitor should kick off at ph 6-6.4 and on at 6.5-6.8, that is my understanding and as for your md it should hold at ph 7.8-8.3 with your lights coming on and off.

Mostly everyone on here will agree or have the same standards in mind, if you already have kalk dripping into your tank it should balance it out.

really it's up to you but if your reactor is not holding a 6-6.8ph then the calcium cannot melt therefore not meeting the demands of your tank.