Well thats fosure what appears to be Calcium build up from very "hard" water. Take a sample down to your local pet store and have them test it, if fish can live in it then so can the girls. If thats not an option, get a mail off water sample kit. See whats in your water, or switch over and buy an R/O unit.
If that deposit is hard and not slimy, and your using a coco blend nute line so there is a bunch of Ca added to it already and then if you add cal / mag then you have severely overloaded the water with calcium and it will precipitate out and accumulate very quickly on all your hydro parts...pumps included. Hope you find the problem quickly.....always a PIA when you have a problem you can't seem to get to the bottom of.