My husband and I broke down the DE filter, cleaned it out, backwashed, blew the lines, replaced the DE filter and the pump is still running slow. It starts out running great, (around 23) and then the water slows down from the return valve. Not sure what else we need to do to keep it running great for more than an hour. I go out to bump the filter every hour to keep the pump running good, just am not use to the pump/filter slowing down so quickly. Any suggestions?