Model # R20841-6
Cal-Shock 65 – Fast-Acting Calcium Hypochlorite Shock
Powerful Pool Shock Treatment for Crystal Clear Water
Power Blast® Cal-Shock 65 delivers a quick chlorine boost with 68% Calcium Hypochlorite and 65% available chlorine. This fast-dissolving granular formula wipes out organic contaminants, algae, and bacteria—making it ideal for weekly maintenance or spring pool openings.
✅ Key Features
➡️ High-Strength Formula – 68% Calcium Hypochlorite, 65% available chlorine
➡️ Fast-Dissolving Granules – Works quickly to sanitize and clarify water
➡️ Effective Shock Treatment – Great for weekly use or after heavy pool traffic
➡️ Convenient 1 lb Bags – No measuring, easy to apply
➡️ Spring Start-Up Ready – Quickly restores water clarity after winter
➡️ Made in the USA – Quality and reliability you can trust
✅ Usage Tips
➡️ Balance water chemistry before application
➡️ Apply in the evening or when sunlight is minimal
➡️ Follow dosage instructions on packaging for best results
� Mobile-Friendly Dosage Guide
Weekly (Clear Water)
✅ 10,000 gal – 1 lb
✅ 20,000 gal – 2 lbs
✅ 25,000 gal – 2.5 lbs
✅ 30,000 gal – 3 lbs
✅ 35,000 gal – 3.5 lbs
✅ 40,000 gal – 4 lbs
Green Water Treatment
✅ 10,000 gal – 2 lbs
✅ 20,000 gal – 4 lbs
✅ 25,000 gal – 5 lbs
✅ 30,000 gal – 6 lbs
✅ 35,000 gal – 7 lbs
✅ 40,000 gal – 8 lbs
⚠️ Important: Always follow manufacturer’s directions on the product container. Store unopened bags in a cool, dry location.
➡️ Shock your pool back to crystal clarity with Cal-Shock 65.
Order today for fast shipping and dependable water care.
I'm looking for pool shock to sanitize my drinking water. Will this work?
Reply
I have heard of people using pool shock to sanitize drinking water but I can not promote the use of any pool shock for this purpose. You will want to contact the NSF for further information.
Reply
My water is turning green. I had my water tested and it shows 5 on the total chlorine and 0 on the free chlorine, what can I do?
Reply
Chlorine in water may be present in two forms, free and combined. Free chlorine does the hard work of killing bacteria and oxidizing contaminants. When you add chlorine to water, you are actually adding free chlorine. When the free chlorine combines with contaminants, it becomes combined chlorine, or chloramines. This form of chlorine has very little sanitizing ability, and no oxidizing ability. Total chlorine is just the sum of both combined chlorine and free chlorine. You may have what is considered chlorine lock. Chlorine lock can occur in swimming pools where the chlorine in the pool is rendered inactive, even though you may have a total chlorine reading in the pool. In essence, a chlorine “block” means that the chlorine in the pool is literally being blocked from doing its job by other chemicals. The quickest way to resolve a chlorine lock issue is to partially drain and refill the pool.
Reply
Can I add shock through my automatic chlorinator?
Reply
No, you should never add shock through an automatic chlorinator. Never mix different types of chlorine. Pool shock can be added to a bucket of water and poured directly into the swimming pool.
Reply
I have an in ground pool with a mesh winter cover. Several weeks ago, I had added 2 gallons of chlorine to the pool. Since then, with the mesh cover still on, the water has turned green. I've been adding about a gallon of shock each week without improvement. Should I continue adding shock to the pool or should I wait?
Reply
I would recommend waiting until the pump and filter are running again before adding any more shock to the pool. Algae needs two things to grow: food and light. With a mesh winter cover, the algae has more than enough light to grow regardless of the shock that you're putting in. Also, shocking the pool without circulation can cause bleaching of the pool surface
Reply
My pool company recommends using a phosphate remover. Do you have any such item?
Reply
$58.99
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The Most Helpful Review
11 0
(4 out of 5 stars) Get ready for economic collapse :)
Reviewed By: Mike from MA ()
Purchased this product for drinking water purification. Good price for what I was looking for. Make sure you know how to use this stuff if you're planning to use it for drinking water.
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The Most Recent Reviews
3 0
(5 out of 5 stars) Best pool Shock on the market
Reviewed By: Robert M. from Southington, Ct ()
Pros: Fast desolving
I am happy I switched to Zappit Pool shock, it out performs all the others.
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(4 out of 5 stars) Great pool shock
Reviewed By: Izzy from Woodbridge, VA ()
Pros: works great!
shock works great. it was delivered very fast too! will buy again.
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(5 out of 5 stars) Great way to start opening your pool!
Reviewed By: Great replacement part from Arab, AL ()
Extremely fast shipping!
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1 0
(5 out of 5 stars) Great Pool Cleaner
Reviewed By: Jody N. from Manton, MI ()
Pros: Individually packaged in one pound. Easier to store.
Awesome product and shipping was very quick. You can not get this high of a quality product at the big box stores.
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2 0
(5 out of 5 stars) Clear as crystal
Reviewed By: Robert R. from San Diego, CA ()
Pros: water clarity
My personal standard for water clarity is my dime test. I have a dime epoxied to the bottom of the deep end of the pool. If I can clearly see the face on the dime, then the water is clear. Zappit Pool Shock gets the job done using less shock than other brands. Costs less, too.
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(5 out of 5 stars) Excellent Swimming Pool Cleaner
Reviewed By: David C. from Muncy, PA ()
Pros: Easy to use
This pool shock worked very well for me and I would highly recommend it.
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1 0
(5 out of 5 stars) Quick service
Reviewed By: Shekhar M. from Chico, CA ()
Cal Hypo arrived as promised, and in a timely manner. No complaints!
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