Theoretically, the kalk would be 'good' for an infinate amount of time depending upon the amount of dissolved CO2 in your RO/DI water. I do however,suggest that about monthy, the reactor is drained and refilled. Then again, using ESV brand kalk, I get almost totaly dissolution. So then that does not become a problem. I will tell you that I do put a john guest shut off valve on the input of the reactor so you can easily change out the check valve line and rinse the reactor out. Plus it is made even easier with the lid being CNC cut with key holes. So I do suggest if your not using a very high quality kalk like ESV that you turn off the valve, remove the feed line, insert a drain line and pour some water in to rinse out the bottom of the reactor. In summation, add kalk monthly if using a good kalk, or rinse and add kalk monthly if using pickling lime or such.