Old Pool to a New Owner

[PoolDoc]

Looks like this is what you are looking for:

Waterway Pro Clean 100 => Unicel C-8409

Unicel specs are 8 15/16" OD; 17 3/8" long;

The pressures you report are consistent with a collapsed filter. I'd recommend getting two cartridges and swapping them out whenever pressure climbs to 5 psi above initial. Once you get the cartridges, use this guide to cleaning them:
Cleaning-your-Cartridge-Filter-wiithout-Damaging-It!

[TonyIsSocial]

Purchased 2. I'll post again when installed with psi readings.

[TonyIsSocial]

Pleatco was at 4psi
Unicel cartridge installed and at around 3psi.
Pic of both side by side is with pleatco after running 2 days after being sprayed off.

Dumped bag of shock I mentioned before Sunday night as I was starting to notice algae growth. FC currently at 3.2ppm

[PoolDoc]

Do you notice any difference between the cartridges? Is the filter material in the Unicel stiffer? Is the Unicel company name stamped or molded into the end pieces?

[TonyIsSocial]

Yes, stiffer. UNICEL was stamped on the end piece. The pic is of the label.

[PoolDoc]

If you think to do so, I'd love to have you post a follow-up in a month or so.

[TonyIsSocial]

Will do, thanks! Can you verify my account?