I would get a calcium reactor and a kalk reactor vs getting dosing pumps. I choose this route because it only cost me about $40 a year for c02 and new media,to keep up with 450 gallon reef system. I can't imagine what I would spend on 2 part. Ive been using the same calcium reactor since high school and Im 42 now, so would say its stood the test of time pretty well. I don't see the downside to a calcium reactor on a 300 gallon system.