Read the description. Dont know why but this is stabilized shock which makes no sense to me. Stabilizer in this shock concentration jacks up your cyanuric acid (CYA) readings and the ONLY way to reduce it back is by draining and refilling water in proportion to amount you need to reduce CYA by. You want non-stabilized shock, so it does its thing and goes away letting your regular chlorinator (with stabilizer) do its thing. CYA does not evaporate. My CYA shot up to 160 before I realized the shock was stabilized. 30-50 is normal. Higher than 50 actually inhibits the chlorine from doing it's sanitizing work. I had just converted to salt a week ago, and now I need to drain 75% of my water out to get CYA levels down, and reset all my other chemicals. Not happy.

I have bought shock from Sam's for years and never had an issue. This year I used two bags one day, and two bags the next day. My Cyanuric acid level went to 290. I was reopening my pool so the shock was the only chemical in the pool. I have a large pool and I had to drain about 6000 gallons and refill with fresh water to get the level back down to 78. I will be going to Sam's club today to ask If I can return the unused portion of the box. This is the first time I have had problems with shock bought from Sam's. I will not be using this product in the future.

Something changed with this years formula....i have gone through a full box in two and a half weeks it will not bring up my chlorine levels even when combined with the chlorinator using members mark tabs. Ive been maintaining my pool the same way for years and have had 4tests from leslies in the last two weeks. This last test even with putting 3 bags of shock in is showing very low chlorine and they recommend another 3 bags.... The big issue i think is the 55% available chlorine in this versus leslies brand or other top tier brands. Two cousins having same issue....one put one bag of the Leslie's shock in and raised chlorine levels by next day. Prior to that like me he went through about 6 bags of this garbage in a week. Im going back for a refund

Like many other reviews, I have found that this adds cyanuric acid to your pool so fast that the chlorine you add has no effect. I started with 90, replaced almost 10 inches of water, added this product and now it's so high it's off the scale. I'm sticking to chlorine bleach - $2.50 a bottle for concentrated (8.25%) and there's enough cyanuric acid in there now to stabilize for decade.

Not sure why all the bad reviews on this. It is for chlorine levels, not ph or alkalinity. Different products do different things obviously. Do some research on how to get other your other readings up to standard. This works great for shocking your pool

Have had all kinds of problems with my pool since I started using this brand of shock. Seams to take 3 time as much to change the combined Chlorine level, which will raise the cyanuric acid to a way to high level. Will never buy again. Bring back the original brand.

Never had problems with our pool until now. Using this allowed mustard algae to grow with reckless abandon in our pool even with triple shocking it. Didn't realize how counterproductive it was to continue dumping copious amounts of this garbage into the water in our attempts to rid the algae. We've barely been able to use our pool this summer because our weekends are spent scrubbing the walls and scratching our head about what has happened to our beautiful crystal clear water. Wish I would've researched this stuff before wasting any time and money. JUNK! DON'T POLLUTE YOUR WATER WITH THIS JUNK!!

Use once a month for great pool disinfecting

Product OK but price has DOUBLED in less than a year and the box looks like it's 10 years old!

Great to be able to order online and get free shipping!