Sand filter changed @ start of season ? HIGH PRESSURE @24 PSI FROM START

[timmygreene]

I noticed at start of season I'm building pressure on both recirculate and filter positions. I noticed when I started up the filter I backwashed so I could fill water in the sand filter. Then I rinsed then I went to filter mode, the pressure started at 24 psi. on the new guage. I thought from last season my guage was faulty not the case. Any ideas on why? I have A 18 x 36 inground pool with heater. When A filter needs to be backwashed the water flow is weak this is what happens on both filter and recirculate positions. But the flow is great at the start of either position, just as it runs it get a weak flow to the pool.