Liquid Reactor by Kent works the best!
I have been dosing with Kalkwasser for a long long time and over the last 12 months or so I have had troubles hitting over the 350ppm mark.
Just yesterday I was given a bottle of LR, you have to be careful not to overdose but this stuff works excellent. I was sitting at around 280ppm then added one capfull and two hrs later I was at 440ppm
I will now test the Ca daily for a week or two in order to find out how much depletion is taking place.