Jeff,
Given what you have just posted, I would do a few things if I had the same situation.
Salt: I have read good things about Red Sea Salt on Reef Central. It is used a lot in other areas of the country. Can't comment on it personally, but I think it is held as a higher quality salt than say, Instant Ocean, which is what I use. Go to other areas of the country and and folks aren't familiar with Salinity either. I don't think a KH of 14 in new saltwater is that big a deal either. We all know that KH is one of the highest fluctuating levels we test for, and if it is 14 new, it will drop soon enough when it hits your tank.
I think your issue lies with your calcium reactor being new and not being dialed in. Make a choice in your salt brand, stick with that, and then you adjust your reactor to the particular chemical characteristics of the salt/DT system.
Reactor: narrow your RKL reactor hysteresis setting to the narrowest band there is. You pick a pH setpoint, then set .01 units as the hysteresis, so your current setpoint is 6.8, so your CO2 will turn on at 6.9 and go off at 6.7. A narrower hysteresis will give more control over the output of the reactor effluent.
I have found it is easier to set a drip rate and a bubble count and stay with that, and only adjust the reactor setpoint. About 1 bubble CO2 per second and about 60 ml/minute effluent rate is a good starting point. Doesn't need to be exact, just cloes to those points.
Assuming you have a consistent CO2 bubble rate and effluent rate, the relationship between reactor setpoint and KH (bicarbonates)/Calcium/magnesium released from reactor is inversely related. The lower you set the reactor pH setpoint, the more media you dissolve and the more KH/Ca/Mag will be released (more carbonic acid formed from the CO2 to dissolve the media). The higher the reactor setpoint, the less KH/CA/Mag released (less carbonic acid formed from the CO2 to dissolve the media).
IIRC, you are not heavy into SPS or other high calcium consuming animals, so I don't believe a second media chamber is really necessary for your setup. The net effect of the second chamber is it will add some extra alkalinity/calcium and mag to your system as the low pH effluent from the first chamber runs through it. If you remove it you may find you need to adjust your reactor setpoint down a bit, say from current 6.8 to 6.7 or similar. A single chamber would give more control over the effluent and how much media you are dissolving. Don't worry about pH in your system, not really important, as long as it is between 7.8 and 8.4.
Test Kit: go buy a Salifert KH test kit, and stop worrying about variances between different brands. Salifert is a great kit, IMO, and they give you a reference solution to test against. Pure Reef sells Salifert, around $20 I think for the KH test kit.
What I would do:
1. pick a salt brand and stick with it.
2. manually adjust your calcium to 450.
3. go get a Salifert KH test kit.
4. Change your RKE controller setpoint to the narrowest hysteresis allowed.
5. remove the second chamber from the reactor setup, then wait two days to test for KH with the Salifert test kit.
6. set bubble count and effluent rate to the above suggested rates and keep them there without playing with them.
7. Test System (tank water, not reactor effluent water) KH daily at about the same time. Based on readings, aim for a KH of about 9. If your KH is higher than that, reset the ca reactor setpoint (midpoint) up by .01 units of pH, like from 6.8 to 6.9. If KH is lower than 9, lower the reactor setpoint by .01 units of pH, like from 6.8 to 6.7. Wait 24 hours and repeat KH test and adjust again if needed. Do this until your reactor maintains system KH at your required level. Remember, lower reactor pH setpoint=more CO2=more media dissolved=higher system KH, and higher reactor pH setpoint=less CO2=less media dissolved=lower system KH.
