Eco-system (aka Swamp!) living in my pool...

[The Boyd Family]

Getting extra cartridges will make the work easier and faster and more pleasant. You'll also be much less likely to destroy your cartridge. Looking at your filter,

CLEARWATER II Cartridge. FILTER INSTRUCTIONS - Waterway Plastics

it appears that this

Unicel C-8409 Replacement Filter Cartridge for Waterway Clearwater II 100

is the correct cartridge.

If you can get 1 - 2 cartridges, and have one cleaning all the time;

Cleaning-your-Cartridge-Filter-wiithout-Damaging-It!

it will make the work much easier. Make sure to compare dimensions on YOUR cartridge, with the one at Amazon, to verify that it's the right one. If you order elsewhere, make SURE to get a cartridge MADE BY Unicel or Filbur (not "fits" or "replaces"). All of the Asian made cartridges we've encountered (incl the very common Pleatco, as well as the OEM Intex cartridges) are very inferior in quality, and do not perform well.

As Watermom told you, you'll need the K2006, once your water begins to look like pool water. Meanwhile, the cheap local kit I mentioned above will meet your needs.

Watch out for pool store advice, and do NOT add:
+ algaecides;
+ phosphate removers;
+ stabilizer (if you by dichlor -- if you use bleach it's OK)
+ calcium
+ clarifiers or flocculants.

Do physically remove as much 'goop' as you can. Do run your filter 24/7. Do clean your cartridge once filter pressure goes up 5 psi over clean pressure.

Good luck!

PoolDoc, I ordered the filter that you linked to above and it arrived today from AMAZON and the box says it is a 90sqft filter. We currently have a 100sq foot filter installed. Are you sure that this is going to be okay in my unit?