Backwash pressure drops off?

[Macboy]

Hello again all, and welcome to another season of TroubleFreePool for me! The iceberg vanished today finally so I opened my pool today. I gave it a good vacuum and then tried to backwash the filter to finish the job. The pressure came on like a firehose as I've become accustomed to and I did the "chase bugs bunny down the hose" so I can watch the dirt come out and watch for clear water but by the time I got to the end the pressure had fallen to easily half of what it should be. Usually it's blasting out to the street.

I've done some searching and see that step one for me will be a deep clean but I was wondering if someone could explain to me what's happening (assuming the deep clean is the fix) in my sand filter to cause the pressure to start full bore but then drop off to nothing yet run fine as can be in rinse and filter mode? Is it possible that something bloomed in the sand over the winter? The sand filter is kept in a 10 degree celsius garage over winter.

I'll check my chemistry again in the morning and report back - not ruling out just doing a season starting SLAM just to get on good footing all around but we'll take things one step at a time here. I'm more curious what is physically going on inside the filter so I can understand this better.

Happy to be back and opened the pool with confidence thanks to TFP!

 

[Texas Splash]

I agree it's time to take a peek inside the filter. Perhaps there's a large load of sediment on the top of the sand that is interfering with good water flow. Let us know.

 

[Bperry]

Any chance your pump speed dropped and caused the flow change? My pump switched to high speed whenever I turn it off/on, then after a minute If running goes back to it’s programmed lower speed.