Cheap granular chlorine-what to stay away from

First post from me as required. Looking for lesser expensive granular chlorine 25 to 50lbs. I think that I should be looking for 99% sodium dichloro-s-triazinetrione dihydrate with about 56% available chlorine. Prices are all over the map from Leslies to Lowes to Sams. Which brings me to the Sams "PoolBrand" granular chlorine that has the exact same ingredients as the "good stuff" with claimed 55.5% available chlorine. It's pretty cheap for 50 lbs, but I wonder what I am getting, and will it really be as good as a name brand like "Regal" or Leslies branded "Chlor Brite"? I would do a search before posting this question, but I have to have one successful post before I can search...sorry!

10,000 gal. chlorine/DE filter pool

I doubt very much that you want to get that much Dichlor. The following are chemical facts that are independent of concentration of product or of pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

So if you use Dichlor, your CYA level will climb quickly unless you have a HUGE amount of water dilution. At a usual daily chlorine usage of 2 ppm FC per day, using Dichlor as your chlorine source has the CYA increase by around 55 ppm PER MONTH! Even using Trichlor tabs/pucks (or granular) would have the CYA increase by 36 ppm per month.

Higher CYA levels lower the active chlorine level that kills algae and bacteria. You would need to raise the FC level proportionally as the CYA level rose in order to maintain the active chlorine level to prevent algae growth and that soon becomes impractical.

The solution is to use chlorinating liquid or bleach as your primary source of chlorine once you are at the CYA level you want (you can also add CYA to the pool via pure CYA as that is faster to do than waiting for it to rise from chlorine additions). The main downside to chlorinating liquid or bleach is that you need to add it every day or two. There are several automation options including the use of a peristaltic pump, The Liquidator, or a saltwater chlorine generator. If you use a pool cover that is more opaque or don't get a lot of sun on the pool, then you can add the chlorine less frequently -- in my pool with a mostly opaque pool cover I add chlorine twice a week.

chem geek is right about using dichlor as a primary chlorine source, 50 lbs would put about 300 ppm of CYA into your 10000 gallon pool. But, to your question, Sam's pool brand is, as best as we know, the good stuff. What you're getting with it is a good deal.