90 gal Corner Pentagon

[rocketlily]

Just did some testing and I found I have problems with the Calcium and Carbonate Hardness levels. I am using a one year old Hagen test kit. The Calcium level is at 300 and the Carbonate is at 80 mm/L (ppm). I do have Seachem Reef Complete for raising calcium, but if I'm understanding things correctly, this could reduce my alkalinity levels. What to do?

I am trying to keep this simple, without adding all kinds of extra equipment. Your advice would be much appreciated on this.