Why Does My Spa Feel Slimy? How to Fix a Slippery Hot Tub

Jennifer Rhodes

By Jennifer Rhodes · Updated

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Who doesn't love spas and hot tubs? They are great for sore and aching muscles—even during the colder months—but it's essential to keep them properly maintained.

If not clean and correctly balanced, they can cause a range of health issues (for both you and the spa). If you're coming up against a common problem like slippery feeling water—or noticing a nasty white film on your hot tub walls—you may feel like you're at a dead end.

Rest assured a slimy hot tub may not be any fun, but it is fixable. First, let's identify the cause of the slime.

What causes slimy or slippery water in your hot tub?

1. Biofilm

The most common cause of slimy water in your hot tub is a bacterial substance called biofilm.

This is caused by bacteria that grow in the warm water of your hot tub. They can live in the piping of your hot tub, on interior surfaces, or in the filter.

Their byproduct is a greenish-white sticky residue, which usually shows up as a white film on hot tub walls. It can also cause slippery feeling water that makes it hard to sit in your hot tub and truly enjoy it without feeling icky (it can smell bad too).

2. Mold or algae

Another cause that might be a bit more obvious is algae and mold. This is usually something that you can clearly see in the water and on the interior of the hot tub, and thankfully, that you can remove.

Mold, mildew and algae grow in water that has not been adequately treated to prevent these issues. If you treat your water properly, you should not have to worry about algae and mold forming, even if your hot tub is not in frequent use.

3. Scale buildup

If you have hard water, or if pH is too high in your hot tub, this can lead to mineral buildup.

If the pH is not kept within the safe range of 7.2-7.8, it becomes alkaline and can deposit a hard white scale that is not only uncomfortable to sit in, but also uncomfortable to look at and to feel on your skin. This can also cause build up on critical parts and can cause damage to your filter, spa and its internals.

Most people describe scale as feeling like sandpaper rather than slime, but I'm including it here as another thing to look out for.

4. Chemical imbalance

The last issue you might be coming up against is water that has not been properly treated. If there is too much of some treatments or chemicals in your water, it can feel slimy and unpleasant to sit in.

One particular thing to check is if you're using borates. While these are great as a pH buffer and can help your water feel softer, too much could lead to a slimy feel.

Did you know? Hot tubs, though they are much smaller than a pool, actually require more treatment and care to keep water balanced at the right levels—and to ensure that the right type and amounts of chemicals are used to keep the water clean, sanitized and safe for use.

The good news is that these problems are all extremely common. There are easy fixes you can apply to get rid of that slimy feeling, and solve each and every one of the problems we have discussed so far.

How to fix common issues that are causing a slimy spa

How to remove biofilm

As a sticky substance that can grow in both the visible and invisible parts of your spa, biofilm is notoriously hard to remove.

To remedy this issue, you unfortunately need to drain the water and start over, using a jet and pipe cleaner to dislodge any hidden biofilm. I wrote a thorough guide for how to clean inside your jets and pipework which goes into more detail.

This is going to kill any bacteria that might be present.

Fully removing all traces of biofilm is the only way to prevent new bacteria from immediately growing and forming new biofilm.

After you've refilled the spa with fresh water, staying on top of your regular maintenance each week and keeping sanitizer levels up should keep bacteria from coming back.

How to remove algae

The best way to get rid of algae is again, to clean your hot tub.

You might need to fully drain the spa if you have a severe case of visibly green water, but in other cases, shocking your water and cleaning your filter and changing it out can be enough to get rid of the algae and mold in your spa.

With regular shock treatments, keeping your filter clean and changed as needed, and paying attention to the spa and to what the water looks like, you can keep algae and mold at bay.

How to fix scale buildup

To remove scale, you'll need a scale remover like this one on Amazon. If it's just a little scale in areas you can reach, you can apply some of this and scrub the scale to remove it without draining your spa.

If the problem is worse, you'll want to do a full drain, thoroughly scrub all the scale off, and then use a jet and pipe cleaner to flush out all the internal workings of your spa.

To monitor pH levels better in future and prevent this problem from happening again, your best bet is to buy a small testing kit or strips, and to test the spa water at least once a week. The pH levels of your water can be thrown off by certain other chemicals, by adding new water to the spa, or by people getting in and out and introducing substances like body oils or lotions.

If you find that your pH is too high, you can use a pH down product like Leisure Time Spa Down. If it's too low, you need pH up instead—the equivalent Spa Up will raise it.

How to fix chemical imbalance

The last issue you might be dealing with is water that has not been treated properly. If your water does not have enough chlorine or bromine, if borates are too high, if the pH if off balance, or plenty of other things, these issues can all lead to water that feels less than desirable on the skin.

This is topic too broad to cover in detail here, but our easy maintenance guide is a good place to start. Essentially, you need to test your water often and make sure that you are adding the proper chemicals to keep your water balanced and clean.

If something is off that you can't correct with other chemicals, you can always replace some (or all) of your spa water and start over with a fresh fill.

Top tips on caring for your spa properly

So, there are a few basic things that should be done to care for your spa and to help prevent the dreaded slime from coming back in the future.

  • You first need to make sure you sanitize the water, usually with either chlorine or bromine. Bacteria can come from anywhere, and can grow in all sorts of forms, making the water slippery and unsanitary if left to get out of control.
  • Next, you need to regularly clean your filters and wipe down the surfaces of your spa and cover to get rid of any algae and mildew (a simple bleach solution works great for a weekly wipe-down). The goal is to maintain water that is safe for you and your friends to be in but not habitable for bacteria, algae and mildew to grow or form.
  • You also want to check your pH levels and make sure that they are in the safe range of 7.2-7.8. Acidic or alkaline water is not safe for skin or spa parts, and water that has too high of a pH can cause scale to form.
  • The last thing you need to keep in mind is that a spa is the same water circulating until you drain and refill. This means that the water needs to be fully replaced every 3-4 months, and regularly treated in the mean time to prevent things from growing and living in it, and to kill bacteria as quickly as possible.

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