Newbie with a 21' AG pool, wondering about copper

That looks exactly like my filter. And it's the 28" one too. Is there a difference between those two filters?

And I've not been able to find plain liquid CYA. I've found a granular one, but the guy at the store says that it will just clog up my filter before it actually dissolves (2-3 Days). So he steered me to a liquid "CYA" that turns out to be monosodium cyanurate monohydrate. I'm assumed that the guy was full of it and left. So, are the granules OK? should I dissolve them in water first then add? My searches here did not find anything positive about monosodium cyanurate monohydrate, so i might be skipping liquid and going granular.

My test kit should be here soon, so I can get some more accurate numbers.

And thanks for all the help.

CYA *will* sit on your filter for a few days, but it won't clog it.

Liquid CYA is based on the sodium salt of cyanuric acid you mentioned. A cheaper and easier way to add CYA is simply to chlorinate with dichlor granules for the first few weeks. For each ppm of chlorine you add that way, you also add almost a ppm of CYA! As long as you NEED cyanuric acid, this is a very good deal, both in terms of price and convenience.

If you have access to a Sams Club, their PoolBrand undiluted dichlor (50# bucket; 24# box) is usually the best deal going. But I'll post links to Amazon, in case you can't use Sams Club. Most other stores -- Costco, Walmart, Kmart, etc -- sell diluted dichlor.

To use dichlor, just add doses to the skimmer, with the pump running. With 13K gallons, a reasonable dose would be 1 pound (about 2 cups) in the skimmer each evening. Each dose will add about 5 ppm chlorine and 4 ppm of stabilizer. Once you have added (5) doses, you'll have enough CYA in the pool to have an effect.

Have you ordered a K2006 test kit, yet? Regardless, get a cheap OTO/phenol red kit, and adjust your dose the following evening, based on pH and chlorine levels.

Regarding your filter, apparently Water Way made two models of that filter, and you have to match replacements by length.

Here are the Amazon dichlor links:

PoolBrand granular dichlor 50lbs @ Sams Club => ~$2.20/lb (May 2014 in Chattanooga)
PoolBrand dichlor bagged shock 24lbs @ Sams Club => ~$2.50/lb (May 2014 in Chattanooga)

Kem-Tek dichlor 22 lbs @ Amazon => ~$3.50/lb (May 2014)
Kem-Tek dichlor 12 lbs @ Amazon => ~$4.10/lb (May 2014)
Kem-Tek dichlor 5 lbs @ Amazon => ~$5.00/lb (May 2014)
Kem-Tek dichlor 2 lbs @ Amazon => ~$9.00/lb (May 2014)

Keep in mind that Amazon products normally ship free; and that in many parts of the country, you will not have to pay sales tax. Shipping + tax can increase the cost from other suppliers by 15 - 40%, so compare delivered cost, not nominal price.

KemTek brand products may also be available at local Home Depots; match pictures here to what you see at Home Depot, before you buy. Otherwise you may end up with diluted dichlor there, too.

If you don't want to use the dichlor, it is perfectly fine to use the granular CYA. I have done so for many years without a problem. You can slowly pour it into the skimmer while the pump is running and then just leave your pump running for the first 4 or 5 days after adding it while it is dissolving. Don't retest your CYA level for about a week after you add it to make sure it is fully dissolved and in the water to be able to be detected or else you are just wasting your reagent.

Ok I picked up a box of PoolBrand dichlor bagged shock from Sam's today. When I got home about 1:00, I tested and the test said 0 CC. So I added one bag and waited a few hours. Then I got a surprise around 5. My K2006C test kit arrived. So I can now post my numbers.

So here are my numbers from the new test kit. If I did everything correctly
FC=.66
CC=0
PH=7.8
TA=120
CYA=0

OK, need a little more chlorine.

Don't overtest CYA -- you'll run out of reagent.

How can the chlorine reading be 0.66?? Maybe meant 6.6 instead?

I thought something didn't seem right with my chlorine levels. So I checked again and my math was off. I multiplied by .02 instead of .2.

So my FC is 6.6, but my CC is still 0.

CC of 0 is good. That is what you want! :)

I tested my water today and my FC was 4, CC was 0 and CA was 40. I picked up a box of the 1lb dichlor bags from Sam's. I have been using that for the last couple of days.
How fast does CA usually drop? Should I continue to use the dichlor or do CA levels stay good for a while?

CYA is lost from backwash, splashout, and sometimes bacteria will consume it if chlorine is depleted. Once you get it where you want it, it should pretty much stay.