This is an effective pool shock and keeps my pool water clear. This IS a stabilized shock and adds CYA every time you use it. CYA does not lower with evaporation, and increases as you use it, IF Sam's club had another option to shock a pool without increasing CYA, I would purchase this other option along with this product to maintain the pool. The Chlorinating granules that are also available seem to be more for a salt water pool, which is not my particular pool.

I was using HTH brand of shock since having my pool and tried this brand last season. My experience is opposite of most reviews here. Since using this brand I have found that I use less. Out of a 24 lb box I only used 20 all last summer. My pool operation and balance was very easy using this product. It is fast dissolving and tends to work very well. Please note that I use this product before allowing my pool to show serious signs of dirt or Algae growth with much success. Also the cost per 1 lb bag is much cheaper than other brands I've seen although the Chlorine ratio is only 50% per bag I do take that into consideration as well.

Works great, gives a better shock than the generator does. Also lasts longer as it has cyanuric acid with it to stabilize, so don't have to add as much separately. Started using this for weekly to biweekly shocks in salt water pool and works so much better than the generator "shock" does, especially in the summer heat.

We forgot to order the shock we usually do and were at Sam's. We saw the shock and realized it was about $2.50 per lb. That is a very good price. We tried it and even when we didn't jump right on the pool, when we applied it, it brought it back to bright blue overnight. We were even able to get thru spring where we are hit with mustard algae at least once, usually twice for the last 20 years, nothing. No yellow/green color remained when we just used this shock. No special mustard algae treatment was necessary this year. Simply unbelievable for us. It also lasted longer. We do add at night so the the sun doesn't break it down before it dissolves, but we don't have to add much and we have a good sized pool. We are on our way to get another box. Hope Sam's keeps this as a year round product because it works.

Works great for me in 18,000 gal fiberglass pool. Last year, I was struggling to get the pool clear. I finally determined that the sand in my sand filter was shot . As soon as the sand was replaced, the water cleared right up. Chemicals won’t fix every problem.

I have used Members' Mark pool chemicals for several years with good results. This year I have had to used 3 times the quantity in the past with terrible results. I have used an entire box of shock in less than 30 days. After reading others reviews I have learned they changed the formula and manufacturer. Yesterday I went to a competitor and bought their shock which is slightly more expensive than Sams but it immediately worked. Sorry Sams but you lost my business on this one.

Started our spring with this shock and could never get any chlorine readings. Water analysis by two pool stores said to add more shock. Added more and more and more, still no chlorine reading. Finally had enough, drained the pool, went to another brand of chlorine and shock and immediately everything is fine. This product is worthless. And there is no way to take bad chlorine back! Please beware.

Used it last year as a preventative for Alge, had a hard time keeping it at bay, just used the remainder to open pool this year, used 4 bags 28000 gal pool 1 day later pool is still green, sorry this stuff is lousy. will not buy again. Get HTH green to blue or Clorox xtra

Shock works as expected but...the bonus testing strips were missing from the box.

Works well.