I don't know about calcium removers but if your fill water has 0 calcium, drain off 20% and refill and you should be around 300ppm. If your fill water has calcium, you'll have to do some simple arithmetic. Supposing your fill water is 100ppm. Drain off 1/2 of 500ppm and refill with 100ppm. You should get 300ppm.

You may also be able to improve your results by simply lowering your t/a further.

Carl