Cloudy water is one of the most common issues for hot tub owners. I know because I’ve been there many times. But you don’t have to panic. So firstly, what’s causing the water to turn cloudy?
The most frequent causes of cloudy hot tub water are clogged filters, high alkalinity, pH imbalance, low sanitizer levels, high calcium hardness, pump issues, and a biofilm build-up. Entering a hot tub without showering increases the chances of clouding by introducing outside contaminants into the water.
Bathing in clear water isn’t just for aesthetic purposes only. Cloudy water is a sign of sanitary issues that need to be addressed immediately to prevent you from becoming sick.
7 reasons your hot tub water is cloudy
Here is a list of the seven most likely causes of cloudy water in a hot tub. As you read through, you’ll begin to notice how the causes are closely linked to one another.
1. Clogged and dirty filter
Whenever you face an unexpected issue with water quality, the first thing you should check is the filter.
If your filter is dirty and clogged, it won’t be able to filter out any impurities in the water, which leads to water clarity issues such as cloudiness.
Cloudy water can also occur when the filter isn’t positioned properly. When this is the case, the water bypasses the filter cartridge and continues to circulate unfiltered.
2. High total alkalinity
Spa water with a total alkalinity (TA) reading above 200 parts per million (ppm) is a likely cause of cloudy water in your hot tub. This is due to the TA creating an imbalance in the pH levels, which leads to calcium scaling.
High TA levels also cause the chlorine sanitizer to be less effective. When the sanitizer can’t do its job, bacteria multiply and cause your water to become cloudy.
Total alkalinity is the buffer that prevents fluctuations in the pH level. High TA levels make it hard to control your pH and keep it in range, which is why it’s necessary to test and adjust the TA before moving on to the pH.
3. pH imbalance
Hot tub water with a high pH is another common cause of cloudy water. Very high pH levels cause calcium not to dissolve properly, which causes the water to turn cloudy.
Although a pH imbalance isn’t a direct cause of cloudiness, it affects how sanitizers and other chemicals work in your spa water.
Chlorine becomes highly reactive when the pH is low, causing it to rapidly deplete. Because all the available chlorine has been used up, it’s ineffective in killing bacteria and other microorganisms in the water.
A word of warning: If you have persistent issues with your pH levels becoming too high, it’s sign of a bigger problem. I’d encourage you to read through my guide so you can put a stop to the issue for good.
4. Low sanitizer levels
Chlorine is a powerful disinfectant, but its potency decreases over time as it has to fight all the nasty stuff lurking in your spa water.
When the free chlorine levels become too low, there isn’t enough sanitizer to disinfect the water, which leads to chloramines (combined chlorine) forming and the water turning cloudy.
Did you know? ‘Free chlorine’ refers to chlorine that is unused and ready to sanitize. ‘Combined chlorine’ refers to the chlorine that has been used up but is still present in the water. ‘Total chlorine’ is the sum of both.
Because some people have a sensitivity to chlorine or bromine, they try to operate their hot tub with as little sanitizer as possible.
This is fine so long as you’re using an alternative sanitizer such as an ozonator (Ozone generator) or mineral cartridge.
However, when the sanitizer level is allowed to drop below 1 ppm, microorganisms in the water multiply at a faster rate than they’re being destroyed, resulting in cloudy water. This puts you at risk of contracting E. Coli, legionella (Legionnaires’ disease), and hot tub rash.
5. High calcium hardness
Calcium hardness is the sum of all calcium dissolved in the water. Spa water with high calcium hardness levels will turn the water cloudy unless the alkalinity and pH are low enough to compensate.
If you live in a hard-water area, you’ll be all too familiar with calcium deposits on things like faucets, showerheads, and kettles.
If the calcium hardness reading is above 400 ppm, you’ll experience cloudiness and start to notice crusty, white scale around jets and other components and inside the plumbing.
Calcium deposits cause filters to clog and provide an anchor for microorganisms. As we’ve already seen, poor filtration can exacerbate clouding in the water.
The hotter your water temperature, the more scale there’ll be. Scale build-up in the pipes reduces circulation and increases pressure, causing your hot tub to take longer to heat up. Over time, scale will cause the spa heater to fail prematurely.
6. Pump problems and air locks
There are several reasons why your pump may be causing the water in your spa to turn cloudy. The first reason is that you might not be running the pump for long enough each day.
Another reason is that there could be an issue with the pump impeller. Because the vanes on the impeller are very small, they clog easily, which dramatically reduces the flow volume.
Lastly, clouding may occur if the impeller is broken. If the pump turns on but the impeller isn’t moving, there’ll be no flow. When there is no flow, it’s a sign of an airlock.
7. Biofilm in the plumbing
Although not so common, in extreme cases, biofilm can turn spa water cloudy. Biofilm is a slimy bacteria that lurks on the inside of your spa’s plumbing.
It can form rapidly in spas that have been sitting empty for some period of time. You may also notice foaming and slimy flakes floating on the water when there is a build-up of biofilm.
How to fix cloudy hot tub water
Now you’ve identified what’s causing the water in your hot tub to cloud up, here is a list of fixes.
Clean the filter
Remove the filter and rinse with this chemical spray. If it’s been so long since you last cleaned the filter that you can’t remember when you did it, then it’s best to perform a 24-hour chemical soak.
Spa filters don’t last forever. As a general rule of thumb, you should replace your filter every 12 months. If your hot tub sees a lot of use, it needs to be replaced more frequently.
If you can’t get the filter clean after soaking in chemicals, then it’s time to replace it with a new filter.
Also, make sure that you position the filter correctly when reinstalling. The cartridge should be fully seated on both ends to ensure the water is forced through the filter pleats.
The first thing you need to do is to test and adjust the alkalinity. While test strips are useful, I recommend using a liquid test kit for the most accurate test results.
Using a clean cup, collect a sample of water from elbow deep in the center of the spa. Allow it to cool to room temperature before testing.
Add pH decreaser (sodium bisulfate) to lower the total alkalinity to between 100 – 150 ppm. Let the water circulate for at least 15 minutes before retesting.
The optimum range for pH is between 7.4 and 7.6.
While you’ll often see it recommended online to keep the pH within 7.2 – 7.8, it’s better to keep it within the optimum range to give yourself some breathing room should things change unexpectedly.
To adjust the pH, test the water first using the liquid test kit mentioned previously. Collect your sample from the center of the tub and allow it to cool to room temperature.
Depending on your reading, you’ll need to add pH decreaser or pH increaser. Again, let the water circulate for at least 15 minutes before testing the pH levels again.
Rather than purchase all the chemicals individually, I recommend this balancer bundle kit that saves money and ensures you have everything on-hand ready for any unexpected problems.
If your sanitizer of choice is chlorine, add enough to raise the level to between 1 and 3 ppm. Adjusting to 3 ppm is the optimum level for chlorine.
If you prefer to use bromine to sanitize your spa, add enough to raise the level to between 3 and 5 ppm. Adjusting to 5 ppm is the optimum level for bromine.
To give the sanitizer a boost, shock your spa water regularly. This is especially important if sanitizer levels have dropped suddenly or if the hot tub has seen a lot of use in a short space of time.
Spa water may turn cloudy after adding chlorinated shock. This is due to the many chemical reactions that are going on and is perfectly normal. The water should turn clear again within a few hours after adding shock. You can try using a non-chlorine MPS shock to avoid cloudy water.
Lower calcium hardness levels
Test the calcium hardness levels using test strips or a calcium hardness drop test kit (most accurate). The ideal range for total hardness is 175 – 250 ppm.
If the level is a little way over 250 ppm, perform a partial drain of your hot tub water. It’s best to drain about half the water.
If the level is way above 250 ppm, the best solution is to completely drain the hot tub and refill. See my guide if you want to know more information about when to change your spa water.
In both instances, make sure to refill from a hose fitted with a pre-filter. This helps to filter out a lot of the unwanted minerals from the water.
Use this stain and scale control from time to time to keep things balanced and prevent fluctuations in calcium hardness. The product is especially important if you live in a hard-water area or you source your water from a well.
Increase pump runtime and speed
If you aren’t running the pump for long enough, then it’s important to increase the runtime so that the water can circulate and filter properly.
The pump should run on high for at least two hours every day as running at low speed only can contribute toward ineffective filtration.
If there’s an airlock, you’ll need to shut the pump off and loosen the union on the pump to allow the air to escape. Once the water begins to leak, tighten it back up.
If the pump doesn’t turn on, it could be caused by a tripped GFCI button, a bad contactor or relay, or loose wires.
The first stage to removing biofilm is to lower the pH to 7.2. Now use spa shock to raise the chlorine level above 10 ppm. The high chlorine level helps to kill off bacteria and other microorganisms.
You’ll now need to follow this with a line flush cleaner called Ahh-Some. Allow the cleaner to circulate around the plumbing for several hours or overnight to get rid of all that nasty biofilm.
Once complete, drain the water and thoroughly clean the empty hot tub. For full instructions on how to remove biofilm, see my complete guide.