filter appears to be clogging

I have 10-12,000 AG pool with hayward s166t sand filter. The sand has not been changed in probably 10 years (since we put pool up). This year we replaced the vinyl liner and got a new skimmer with new vacuum connector.

When I am using the vacuum, it holds suction, but it does not appear to pick much up.

I have also noticed very poor return pressure. When my PH is low, I often raise the eyeball to aerate the water. This works great after I backwash, but within an hour or so, the pressure is so low, there is no aeration.

I got new hoses to go with my new liner this year, and a few new connectors to the filter. I did not use teflon tape, and I think some of them are leaking. Also, the gasket between the filter and valve may be leaking.

I did notice the filter said flow rate is 35 gpm and my 1hp pump is 60gpm. But I have had this pump for 2 or 3 years. I tend to run the pump 24/7.

Any suggestions as to what my problem may be? Should I open the filter and see what's happening inside? Change the sand?

Try more backwashing? I just realized I never rinse after backwash, so I will try that tonight. I backwash for 2 minutes, even though the glass is always clear.

Both pool and pump strainer baskets are clear.

I don't record the pressure gauge, but it's always around 15-20.

Since it works ok after backwashing, I don't think I have mechanical or debris problems. I am guessing something in the filter or perhaps my small leaks around the fittings.

If the filter pressure rises, flow rate drops and then after backwashing, it returns to normal, that is just the filter filtering something out of the water. Are you sure you don't have an algae bloom?

my skimmer basket was stuffed full of pine needles last night. That tree has to go!
Water is clear, quick check with the oto yellow drops showed fc at least 5. So no apparent algae.

I will keep backwashing and rinsing. I am having trouble getting vacuum seal to clean the bottom. My old attachment is slightly smaller than my new skimmer, and the new attachment that was included with the new skimmer does not have a rubber seal. I will have to get some skimmer socks as well.

Are you getting a lot of pine needles out of the backwash? If not, what is coming out?

I have an in ground drain for backwash, so I never see it. But I think I would see pine needles in the pump basket first, which I do not. I will keep messing with backwash and rinse. Thanks.