If you are new to pool maintenance, learning how to shock your pool should be high on your to-do list. The continuous invasion of algae, bacteria, human urine, sweat, and maybe even poop can turn the leisurely activity of swimming into a hazardous pool of diseases and infections.
Shocking your pool should be a regular part of your maintenance. In fact, we recommend that you do this once a week. You could stretch it to two weeks, but don’t leave it more than that. IT doesn’t take contaminants long to get a foothold, and then you’ll have a larger problem that could take multiple days and several hours of work to fix.
Okay, let’s get the tools together and shock that pool. Here’s what you are going to need!
Pool shock will bleach your clothes, so don’t put on your Sunday best. Find some clothes that you do not mind ruining. Ideally, pool shocking will be a weekly event. Wearing your good clothes is essentially playing a lower-odds game of Russian Roulette, and you will eventually lose.
As you probably know, the sun’s UV light evaporates chlorine very quickly. That’s why it needs a stabilizer after all. Pool shock is generally going to be chlorine. Since you are adding a lot of it without a stabilizer, you will want to add it at dusk. Ideally, the pool will have at least 8 hours without any of the sun’s interference.
Pool shock needs to spread throughout your pool to be effective. Otherwise, you will have a very sterilized spot on your pool, but the rest of it will still be overrun with whatever contaminants that you were trying to destroy.
Most of the time, you will add 1 lb of pool shock for every 10,000 gallons of water that your pool holds. Of course, the product will likely list the appropriate amounts that should be added. Follow the product’s instructions.
Be careful, pool shocking products are very strong oxidizers. They are highly corrosive, so pilling them directly onto a pool surface isn’t a good idea. Letting the pool shock dissolve in a bucket of water will ensure that this corrosive property will not harshly oxidize a single spot. That strong oxidizing power is why we recommend gloves and goggles. Don’t be stupid. Protect your skin and protect your eyes.
Some products say not to pre-dissolve the pool shock. You can follow those instructions, or you can follow ours. We don’t see the harm in pre-dissolving, but there is probably a reason that some of the manufacturers of those products recommend pouring the granules directly into the pool. Use your own judgment and make the call.
Yep, that’s it. That wasn’t so bad, was it? You can stop reading at this point if you want. Everything below is just to let you know what is happening so that you can be more informed. If you stop here, have a great day. If you continue, GREAT! Let’s learn more about the science of pool shocking and answer the common questions that people tend to ask.
To answer that, we need to talk a little bit about chlorine, its purpose, and the difference between free chlorine, combined chlorine, and total chlorine.
When you are adding chlorine into your pool, it generally starts off as free chlorine. Free chlorine is a highly reactive oxidizer with a strong negative charge. It readily binds with bacteria, algae, and any other harmful contaminants by binding with their protein structures, mutating them, and destroying their cell walls. When this happens, they are effectively neutralized and generally safe.
When the free chlorine binds with the ammonia in urine and sweat, those bonded pairs are called chloramines. They are also commonly called combined chlorine.
As counterintuitive as it sounds, a pool that smells like chlorine probably doesn’t have enough chlorine in it. That smell that your nose is picking up is actually from the chloramines. Chloramines are useless, but they generally aren’t considered harmful, just smelly. Of course, too much of anything is bad for you, so you shouldn’t leave them in there. That is where the pool shock comes into play.
This one is actually pretty straightforward. When you add up the free chlorine and the combined chlorine, you get total chlorine. This isn’t too important, but you will end up measuring it to find out how much free chlorine vs combined chlorine you have.
After the chlorine has done its job of killing the bacteria, we don’t need it to remain bonded to those contaminants. “Shocking” the pool is how we break apart those bonds.
Yes, saltwater pools need to be pool shocked too. The chlorine generators go a long way in maintaining chlorine levels, but human intervention is still needed. The chlorine generators are fantastic, but they aren’t adaptive; At least, not yet. Use testing kits to keep an eye on the levels of free chlorine, combined chlorine, and total chlorine. When the free chlorine balance is out of whack or your pool is under attack, add some pool shock to bring it back.
All of this talk about free chlorine begs the question, “How much bleach do I need?” Here is a quick chart that you can use as a basic guideline, but we recommend that you head over to our guide that teaches you how to balance your pool chemicals. The appropriate amount of chlorine depends on multiple factors that are discussed in that guide.
Parts Per Million (PPM)
|Stabilizer||Ideal Chlorine Range||Shock Level|
|30 PPM||4 - 6 PPM||12 PPM|
|40 PPM||5 - 7 PPM||16 PPM|
|50 PPM||6 - 8 PPM||20 PPM|
|60 PPM||7 - 9 PPM||24 PPM|
Unfortunately, it’s likely going to take a lot more effort than a simple pool shock to kill black algae. Black algae is a special case because it technically isn’t really an alga. It’s actually a form of bacteria that is commonly mistaken for algae.
This type of bacteria has protective skeletal growths that protect it from a pool shock. Before you can attack this “black algae,” you will need to crack through that protection with some copper algaecides or some silver algaecides before rubbing the chlorine into its core.
This honestly is going to take a lot of effort, and you will probably need to spend hours over the course of weeks to remove it. If you’re up for it, we actually wrote a tutorial on how to remove black algae from the pool.