How do i know if i need to replace my Pentair 48 plus dns filter grids?

[SQUIGGYCUB]

The filter grids are probably 8 years old. I just cleaned them and they look practically still new. The pressure is reading 20. My heater pump doesn't want to kick in because is reading low pressure. Water in pool always look great.

[PoolDoc]

I don't know any way to test DE filters, and ID clogged grids.

Was the clean filter pressure lower in the past? IF that is the case -- for example, if your filter used to show 12 psi when clean, and now shows 20 psi -- that would be a strong indication that your grids were clogged.

One way that can happen is if you acid clean grids without first cleaning them in detergent, to remove oils and organics.

[SQUIGGYCUB]

The pressure was also 20 before i clean the filter grids. I have never used acid on the filter grids.

[SQUIGGYCUB]

The dirty filter pressure was around 24, and the clean filter pressure is around 20. Normally when the filter is dirty it will read around 30 psi. The heater pump always ran good with a pressure of 20psi, it nows keep reading L PR . I just don't know if the filter grids need replacing or if the problem is in the heater pump. The filter grids looked not dirty at all when cleaned.