I did call in a heavy hitter pool guy, thanks for the insult.. That said, your exactly correct and I just didn't see it at the time I recorded this video as I am a mechanical contractor and not a pool filter professional. The only thing I knew for sure was the customer was backwashing via gravity flow and the delta P across the filter was way out of range. Where were you 9 months when I needed you? I only took care of the boiler that was connected to that pool filter.

so you backwash each filter using the clean water from the other.....im gonna stick with my residential stuff. lol