My house has an AprilAire 550 bypass humidifier (several years old) which has been working well this winter. However, today I noticed a significant buildup of pink "crud" in the transparent plastic humidifier drain tube. The house has a water softener using Morton "System Saver" pellets. The humidifier cartridge is only a few months old and appears normal, not showing any of the pink stuff. The drain tube buildup is not slimy, has no smell, and is soft/mushy to the touch rather than scaley. We had not noticed any brown hard water stains before or after the installation of the water softener last March. This buildup seems to have happened quickly since it's by the washing machine and we haven't noticed it before when washing clothes. I can clean or replace the tube, but I have no clue as to what's causing this. There is no return air grille in the room, but could it be caused by some laundry product we're using? A relative who's a plumber happened to be visiting us and didn't know what it might be. Any comments would be appreciated. Thanks.