I have been having issues with my pump/filter all season. It's a used pump/filter I got from a friend that he had for about 20 years. Here is what happens.
When I run the pump for an extended period of time, the flow rate drops significantly. There are a few things I can do to restore the flow rate.
1. I stop the pump for like a few seconds, and restart it sometimes that works. I also open the air release screw after I turn it back on, sometimes that will work for a few hours, sometimes the flow rate drops again, in another 30 minutes.
2. I regenerate the filter, which I shouldn't have to do since I just put all new DE in (stop the pump, move the bump handle down slowly, lift up quickly 3 times as it states right on the DE filter).
Whats odd is I Just backwashed the filter 3 days ago (really really well, I made sure to get every ounce of old DE out,following the instructions on the filter). I added 4 lbs of DE into the skimmer slowly (as stated on the filter) after backwashing.
I don't understand why the flow rate keeps dropping, its very powerful when it works. It just keeps losing its flow rate for whatever reason.
Final notes, the pool has never been green, not once all season, I've been using clorox bleach every single day and the water is generally crystal clear to very clear, the water is also perfectly balanced, I test every single day so I'm positive its not built up dirt.
The pool was professionally installed only 1 month ago, all PVC plumbing. I made sure that air is not being introduced into the skimmer, however one thing I notice that when the flow rate decreases, the little skimmer trap that is attached the pump doesn't have water up to the cover, I think its because its just not moving water fast enough to fill it up.
I did read something about something within the pump that could need replacing, but I have no way of knowing if that is the case.