Having trouble getting the 24' above ground pool crystal clear....and suspect the 11 year old filter is losing it's grip. DE does not (stay) on the tubes. When I take the unit apart the DE, except for a few clumps at the very top, has gone to the bottom. I'm thinking it might be age has worn them too smooth? I'm using 10-1 muriatic acid to soak it in over night before each new batch and it still falls off. Is this aged out of usefulness?