You are NOT ready to use the PAC, yet. (If you'd like to try it ANOTHER way, and don't mind possibly not getting much value out of $30, go ahead and order. I can help you do a "jar test" -- you'll need a large glass jar, like a big pickle jar. But we can test, and see if it will 'floc' your pool gunk. If it will, you can go ahead and use it, and then vacuum up the floc, to waste. But you'll have to have a hand vacuum, the valves allowing you to vacuum to waste (on the ground) and the time to do it.)

You CAN use the DE, both to test your filter, and to filter gunk. It actually works better on cartridge filter, than on a sand filter, for that purpose.

Is this the filter you have?


If so, check out this manual to confirm it:
http://www.hayward-pool.com/pdf/manuals/Manual135.pdf

Once you've confirmed, you probably should get THIS cartridge:
Unicel C-8610 Replacement Filter Cartridge for 100 Square Foot Hayward CX1100RE @ Amazon

You can get it elsewhere, but make sure you are getting a Unicel, Filbur or Hayward OEM and NOT a Pleatco cartridge. I had to troll through Amazon's list very careful to make sure -- Pleatco markets their filters on an as-if identical basis, when they are not, and some of the descriptions are VERY misleading.

Also, go through the pumps, here, and see if you can find yours:
http://www.hayward-pool.com/ctg/In-G...-1_14002_I.htm

But, we need to ID your pump, we need pictures of your pump and filter -- so I can see your valving -- and we need to make sure your pump and filter are working properly together, before moving to next steps. By the way, do you have a pressure gage on your filter? If not, you need one that works, and we need to know what your pressure is before and after cleaning the cartridge.

Here's a gauge, like you need, if you don't have one:
Super Pro Pool Filter 0-60 Pressure Gauge 1/4" Fitting @ Amazon

You probably can get these locally, and you'll need some Teflon tape for the threads, but a dab of silicone caulk will also work.