ESV is the only kalk mix Ive used so far that didnt leave a tan residue in my reactor, whether the impurities are making it to the tank or not doesnt matter to me, just the fact that they're present is enough to make me choose not to use them. Monitor the effluents Ph, when it drops below 12/12.1-2, its time to recharge... Normal Ph range is in the 12.4-5 area.