Just swap them out each time you change the nutrients and you will have no problem. It's micro or one of the other nutrients that does not break down all the way. LIke B1 or Thrive Alive made from seaweed that is in the water but does not break down that much so it will clog the stones. You just change them out the soak the ones you take out with something like florakleen with air running through them and that will clean them but not leave behind any thing bad for the next time you use them.

Hope that helped.

turtle you crack me up dude .... lol