We have a DE filter, opened our pool and realized the pressure keeps getting too high. We pulled the "fingers" out and had them acid dipped. Reassembled the filter and still have the same problem. Within 10-15 minutes of backflushing the pool, the pressure is back up to 20%. We know it is not the lines because everything works properly on circulate. We have no clue what is wrong and cannot clean our pool until we get this straightened out, any ideas?