How to keep your hot tub chlorine from dropping

hot tub chlorine

You step out of your hot tub, sprinkle in some chlorine, and turn on the jets. After a half-hour or so, you put the cover on and head back inside. But when you go out to the hot tub the next day, it seems like the chlorine has disappeared.

What happened? Afterall, you put enough sanitizer based on the size of your hot tub and the directions on the bottle. Your chlorine levels were within the recommended range before you put the cover on. 

It is normal for hot tub chlorine levels to drop between soaks. However, if the chlorine seems to disappear quickly, there might be an underlying cause.

hot tub chlorine
Why do you have to add chlorine to your hot tub? To keep the water clean! Every hot tub will require sanitizer, and many manufacturers suggest chlorine.

How chlorine works in spa

Chlorine is added to spa water to keep it clean and clear. As the chlorine dissolves in the water, it creates a chemical reaction with contaminants and bacteria. The bacteria is broken down and killed. 

It’s important to add chlorine because it can break down chlorine before it has a chance to multiply and further contaminate your water.

For chlorine to effectively sanitize your water, you should keep the level up between 3 and 5 ppm.

The chemical reaction, during which chlorine breaks down bacteria and contaminants, creates chloramines. These chloramines can cause your water to have a chemical odor. When you test your hot tub water, the total chlorine level measures the chloramines in the water.

Does your chlorine level keep dropping?

Your hot tub water will “use” chlorine. As it reacts to the bacteria in the water, it gets used up. It’s expected that the chlorine levels will drop over time.

But is it dropping too quickly? There are some things to consider.

Balance chemicals

In order for your sanitizer to be effective, other hot tub chemical levels need to be in check. There is an order to balancing your hot tub chemicals and, if you try to just dump in chlorine, it’s not going to go as you hoped. It’s important to first balance your total alkalinity followed by the pH. Once those are in the proper range, you can add chlorine. 

Another thing to consider is the reading for total chlorine. If your total chlorine is too high, you might need to use an oxidizer or non-chlorine shock to free up the total chlorine. 

Biofilm in hot tub

Another culprit could be biofilm and other build-up in the plumbing and components of the hot tub. While you can’t see inside your hot tub plumbing, the one way you might notice the hot tub is if there’s a slimy layer on your hot tub water.

How does this biofilm cause your chlorine level to keep dropping? The sanitizer will spend more time trying to kill this build-up of bacteria in the plumbing rather than the bacteria in your water. 

If you think there’s a biofilm issue, you can use a spa purge product when you plan to drain and refill your spa.

Water temperature

You might be surprised to discover that the temperature of your hot tub water can affect the chemical levels. The chlorine can decay more quickly when the temperature is higher than 100 degrees. If you are struggling to keep your chlorine levels from dropping, you should consider lowering the water temperature when it’s not in use. 

Sun exposure

More often than not your hot tub will be covered. However, if your hot tub water is getting a lot of sunlight, the UV rays can cause the chlorine to disappear more quickly. An offset umbrella, sail shade, or pergola can help filter out sunlight when the spa is open.

Hot tub filter 

When in doubt, check your hot tub filter. It’s the filter’s job to trap and keep dirt and other contaminants out of your water. However, the chlorine will still react to what is trapped between the pleats of the fabric. Your filter should be rinsed weekly and soaked in a cleaner once a month. 

clean hot tub
You want the water of your to tub to be clear, clean, and ready for a relaxing soak. Regularly draining and refilling your hot tub will make it easier to keep chemicals balanced.

Too much chlorine?

Just as your hot tub chlorine can be too low, it can also be too high. If the chlorine levels are higher than the recommended range, it can cause eye and skin irritation. You should not soak in the spa if there’s too much chlorine.

But how do you lower the sanitizer?

Patience is the best method as it should drop on its own. You can also add fresh water to your spa as a way to “dilute” the chlorine. Just be sure to keep an eye on the other levels, such as alkalinity and pH, so that they stay in range.

For a more immediate fix, there are chlorine neutralizer products available. However, it’s important to choose a product that’s for spas. You should never use pool chemicals in your hot tub.