American Marine do a PinPoint meter, its generally regardard as one best PH units, they are fairly cheap, under NZ $100 and have probes that can be replaced. Its the probe the dictates accuracy, and the American Marine probes are standard (BNC connector) and can be used on IKS/OCT/NEPTUNE computers or other PH controllers/meters.
I have 1, its hooked up and running 24/7. I am on my second probe in 4 years, but I will replace it this year. I found after about 1.5years the probes is unaccurate between .3 & .5, which is enough of a swing to make me replace it. Probes are about $35usd.
KH is your ability to buffer your PH, it isn't always an indicator of desirable PH levels, and you should check your PH regulary and you should check it at different intervals during the day, as PH and PH stability are effected with the light cycle of the tank. I check my PH several times a week, and when its out of normal paramaters I check my CA reactor, 9 times out of 10 my bubble count is up/down which is effecting the tanks PH.
Pie