Lee- I have always used the sm122 by milwaukee (never could spell) for my reactors. Its dependable and aforedable, two things i look for when using equipment. Calibrate the probe every 3 months, replace the probe when applicable. Its straight forward.
Jack, not sure what calcium your using or your ca demand but 6.5 may be too high of a p.H. I run my p.H. around 6.2 and am using aquamedic media (essentially, ARM media). If your monitoring your parameters, than disregard the aformentioned.
Hope this info helps.
cheers,
kurt
75gal 6x54w t5's on icecap slr's 3 blue +, 1 pro color, 1 ge 65k, 1 uvl spuer atintic, iwaki 40rlt return, mak 4 on closed loop to om super squirt, mak 3 on etss reef devil, jbj artica chiller, aquamedic calcium reactor, DIY Kalk reactor, DIY media reactor, currently running half phospahte/half carbon.
Live in Uvalde, Texas. On the fish hatchery!