Trying to clean up pool-swamp; Pentair DE filter stops up almost instantly

[Rrb22286]

I bought a house that the pool hasn't been used in 2 years. It was like a swamp I got to cone around well it is now a very light green. Here's the list of things I have done. Changed the grids replaced the top manifold because it was crack.. Recently while in filter mode when I clean out the filter and out new de in the psi starts off at about 15 then raises to about 25 within about 10 mins then to around 30 or more this didn't happen before. Usually stuck around 10 psi for a good hour even when the pool was like a swamp what ciuld have caused this change in pressure.. Right now if I let the pump run for 45 mins there is barely any water coming out of the inlet please help