I ran-short of D.E. the last time I back-flushed awhile ago and just got some in yesterday...meanwhile My Filter Elements seem to have become perpetually plugged-up, for despite My repeated "Back-Flushing" I can't get My system pressure to stay "Normal" for very-long at all...I've read of this situation before - where the D.E. Filter Elements PLUGGED-UP for running the System WITHOUT any D.E. installed ~ but can't remember how they may become cleaned-up to then be "re-started" WITH D.E. properly installed : ?