What is chlorine demand?
Every now and then, your pool can develop an insatiable appetite for chlorine. An intense and unexpected hunger that seems impossible to satisfy. These sudden chlorine demands usually result from an imbalance in the pool chemistry. And in this post, we’ll be covering what causes those imbalances, and showing you how to cure chlorine demand.
How can I tell if I have chlorine demand?
The easiest way to check for chlorine demand is to add chlorine to your pool (use powder or liquid, not tablets). Give the chlorine time to circulate in your water, then grab your test kit.
Test your chlorine levels. If you can’t get a reading, it’s time to shock the pool.
Once you’ve shocked the water, wait the amount of time specified on the packaging of the pool shock, then test your water again.
If you still can’t get a reading, then you’re dealing with a case of chlorine demand. But don’t worry, you’re already ahead because shocking your pool is step one.
What causes chlorine demand?
We know, you want to cure chlorine demand right now. But remember, that in war, knowing your enemy makes all the difference.
Chlorine demand usually comes around during the spring, right at the start of the swim season for many. That’s because when a pool is closed, the water inside doesn’t get a chance to move around much. It becomes stagnant. And when that happens, chemical balance begins to decrease, opening the door to contaminants. This is why some pool owners deal with green algae or cloudy water when reopening their pools.
But this same scenario can also occur with an open pool that hasn’t been maintained well enough.
Another cause of chlorine demand is heavy rainfall. The effect rainfall has on your chlorine levels is dependent on the acidity of the rain where you live. But chances are that if you consistently have trouble measuring your chlorine levels after rainstorms, then you’ve found the root cause.
How to cure chlorine demand
Although it may seem counter-intuitive, the best way to fight chlorine demand is to feed into it. To be clear, you need to supply your pool with as much chlorine as possible in order to make your water normal again.
But you don’t just want to throw in a bunch of tablets. You need fast acting chlorine and a lot of it. So it’s time to shock your pool (yes, again).
To maximize effectiveness, shock your pool at night when the sun is down and incapable of burning away your chlorine. You can read our post on how to shock your pool, but in short, use approximately 3 pounds of shock per 10,000 gallons of water.
Chlorine lock, myth or fact?
First things first: Chlorine demand is a real issue caused by a drastic chemical imbalance in pool water, usually from contaminants or stagnancy.
On the other hand, chlorine lock is the theory that having too much cyanuric acid (CYA) in your water can “lock” your chlorine and prevent it from increasing. But that theory is heavily unproven and essentially false. Although CYA is a chlorine stabilizer, it can’t prevent you from adjusting your chlorine levels to such a severe degree.
Do however keep in mind that some pool professionals will use the term “chlorine lock” when they really mean “chlorine demand”
How to prevent chlorine demand in the future
So now you know to cure chlorine demand, but what about preventing it? The answer is simpler than you think. Here’s why:
Chlorine demand has everything to do with what’s in your water, from chemicals to contaminants. So naturally, good pool and chemical maintenance habits are the best preventative measures against chlorine demand. In fact, sticking to a good pool care schedule almost guarantees you’ll never have to deal with the issue.
But, some cases of chlorine demand arise from stagnant water, usually while a pool is closed. So what can you do to prevent it?
It all depends on how you close your pool.
In some areas, the climate is warm enough for pools to stay open year round. But if you don’t plan to use your pool much during the colder months, you’ll still benefit greatly from running your filter/pump nightly and tending to pool maintenance when needed. This keeps your water balanced and clean, and it’s the key to avoiding common issues like chlorine demand, algae infestations, and cloudiness.
But in places where the winters are cold and fierce, pool owners may want to cover up their pools for the season.
If you want to cover your pool but still run the water:
You need a pool heater that can keep your water heated above freezing temperatures.
Run your filter/pump and pool heater daily to keep your water circulated and warmed. But keep in mind that consistency is crucial here. You must heat and circulate your water daily. Otherwise, expect to deal with freezing pipes and equipment damage when the water gets too cold.
This is why automatic timers are extremely helpful and highly recommended in these situations
[Trying to swim during the colder months? Learn how to use your pool in the winter]
If you want to empty out the lines and close your pool for the season
Try using a Winterpill. It’s a small, clear plastic disc filled with chemicals designed to keep your water clear and pool clean during the winter. Simply drop it in the water when you close your pool for the season, and open it up back up in the Spring without all the extra work.
Closing thoughts
After reading this article, you can rest easy knowing that there is, in fact, life after chlorine demand. All jokes aside, we firmly believe you can cure chlorine demand without a problem. Simply testing your water and treating it accordingly is 90% of the job. The rest is following up with good pool and chemical maintenance. Because do you really want chlorine demand to make another surprise visit to your pool?
Probably not, which is why these resources are perfect for you:
Save time, save money, and achieve pro-level pool maintenance abilities with our pool care schedule
Have another question about your pool? Our Pool Owner Guide probably has the answer you seek
