Maintaining alkalinity levels

[Jim Barry]

I have been having trouble maintaining my alk levels in my tank recently. My calcium reactor is supplying suffient calcium.

My readings are;

Alkalinilty: 5.4 dkh
Calcium: 400 ppm
Magnesium 1500 ppm (minimum).... that was the highest reading available on my salifert test kit

spec gravity: 1.024
ph in tank: 8.08
ph in calcium reactor effluent: 6.5-6.7

Is this level of alk too low?

Is there anything I can do with my calcium reactor to raise the alk to 8 dkh without raising the calcium any higher?

Also, how often should you change the ARM media. I read that it should deplete, however after 6 months I still have pretty much the same amount in the reactor.

Thanks for your help

Jim