What is the difference between chlorine sanitizers and shock? Do you really need to treat your pool with both? You may know that sanitizers and shock have similar chemicals, so it’s common for many ool owners to wonder if you need to add both to keep your pool water clean. Here’s why. 

Shock vs. Sanitizers 

Granular chlorine, liquid chlorine, chlorine tablets and granular shock all have similar active chemicals that sanitize your pool. But the real difference is in the chemical strength and sanitizing power.  

Chlorine sanitizers are necessary for maintaining a healthy pool. Sanitizers provide lower levels of chlorine that can kill organic things like bacteria, viruses and parasites, and they also combine with non-living things (oils, lotions, etc.) which can turn into chloramines (combined chlorine – chlorine that’s already used up). A build-up of chloramines is bad for your pool and your swimmers because they can: 1) Greatly reduce the disinfection power of your free chlorine, 2) Give off a strong odor, 3) Irritate mucous membranes and cause eye stinging.  

That’s where shock comes in. Shock has a more intense chemical strength and is recommended for weekly use. Different from sanitizers, shock products raise the free chlorine level above 5 parts per million for several hours to destroy bacteria, algae and chloramines. Only shock has the power to destroy nasty chloramines.  

Can you shock your pool using sanitizers?  

Unfortunately, chlorinating tablets or sticks can’t raise the chlorine level in your pool fast enough to equal the power of shock. You could use HTH Liquid Chlorine to shock your pool, however you’re going to have to add much more than if you used a dedicated shock product; reference the instructions on the label to ensure you’re using enough to raise the chlorine level above 5ppm for your pool volume.  

Here’s a handy reference to show the differences between sanitizer and shock: 

Daily Sanitizer: 

  • What is it? Chlorine tablets, sticks, liquid or granular that maintains a constant, low level (1 – 4 ppm) of sanitizer. 
  • What does it do? Destroys bacteria, viruses and parasites so pool is always safe and ready for use. 
  • How is it added? Typically added via feeder, floater or skimmer.  
  • How often should I add it? Your daily sanitizers should be present in your pool water every day. Once tablets are fully dissolved, make sure you replenish right away. For granules and liquid, test water daily to ensure free chlorine is consistently between 1 and 4 ppm.  

Weekly Shock: 

  • What is it? Granular or liquid chlorine shock added weekly directly to the pool in the evening. 
  • What does it do? Provides a higher level of chlorine (5 – 10 ppm) that quickly destroys swimmer wastes, algae and chloramines. Ensures clear water while eliminating unpleasant odors and eye and skin irritation. Cal hypo shock formula also prevents chlorine lock. Pool is ready for use the next day or when water test shows free chlorine of 1-4 ppm. 
  • How is it added? Shock should be added directly to the pool water.   
  • How often should I add it? Shock should be added to your pool 1x per week in the evening.  

What kind of shock product should I use? 

It’s important to note that not all shock formulas are the same. You’ll want to make sure you use a calcium hypochlorite (also called cal-hypo) shock formula which doesn’t contain CYA, like HTH® Super Shock! Some shock formulas contain something called CYA which builds up over time in your pool water and can cause overstabilization or “chlorine lock.” That’s when your chlorine is no longer able to properly sanitize your pool water and it may become unsafe for swimming. If your pool is overstabilized, you may notice algae growth that won’t respond to the shock you’re using; or, your water test may show no or very low free available chlorine while all other values appear balanced. Overstabilization is a big hassle to fix because the only solution is draining a portion of your pool water to reduce the amount of CYA, and refill with hose water. When you choose a shock product  

Questions? We’re here to help. You can always call our HTH® Help Line at 1-866-HTH-POOL.