How to Get Rid of Biofilm in a Hot Tub (Step-by-Step Guide)

Is your hot tub water slimy? Biofilm can quickly build up if the water isn’t properly treated, leading to all sorts of problems for you and your spa. So how do you remove biofilm?

A specially formulated plumbing cleaner must be added to the spa water to eradicate all traces of biofilm inside the plumbing and filtration system. Depending on the severity, the cleaner needs to circulate through the plumbing for 1-12 hours. After which, the spa can be drained and filled with fresh water.

Removing biofilm isn’t difficult, but it does require some time and patience. Unfortunately, there are no shortcuts or quick remedies to removing it.

After instructing you on how to completely remove biofilm, I want to show you how to prevent it from coming back so you don’t have to go through this hassle again.

How to remove biofilm

As biofilm forms inside your hot tub’s equipment and plumbing, it continuously contaminates the water as it circulates. The build-up can be damaging to your health and your hot tub.

Read through all the following steps carefully before attempting to remove the biofilm. To avoid future contamination, you must ensure that absolutely no wastewater is left behind.

Remove filters

The first thing to do before adding chemicals to your hot tub is to remove the filters and clean them thoroughly. Removing the filters is also necessary in order to prevent them from clogging as the biofilm remover gets to work.

By sanitizing the filters, you’ll ensure that the spa won’t be contaminated again by any biofilm present in the filters. Give the filters a quick rinse with the garden hose (never use a power washer), and place them in a large bucketOpens in a new tab. filled with diluted filter cleanerOpens in a new tab.. Leave in the chemical soak for 24 hours.

After 24 hours, remove and rinse thoroughly with fresh, clean water before placing it back in your hot tub. Any residual chemicals can cause foaming after restarting your spa, meaning that you’ll have to drain the water and start over again. If, after soaking, you’re unable to get the filter clean, it means that it’s time to replace it.

Add plumbing cleaner

With the filter removed and soaking in chemicals, it’s time to tackle the biofilm. To remove the biofilm in the plumbing, you’re going to add a plumbing cleaner, also known as a line flush.

I like to use this super-concentrated Ahh-Some biofilm cleanerOpens in a new tab.. The specially formulated cleaner breaks down biofilm in the areas that you can’t get to, such as the pipes. Ahh-Some is been proven to be far superior to other popular cleaners such as Oh Yuk, Leisure Time, and BioGuard.

Add one teaspoon per 125 gallons (5g per 600 liters) of Ahh-Some to your hot tub, turn on all the jets, and allow it to circulate for at least one hour.

If this is the first time you’ve used a line flush, or the hot tub has been sat unused for a long period of time, then I recommend letting the flush circulate for several hours or, even better, overnight.

As the plumbing cleaner gets to work, it’ll cause a disgusting-looking scum to form on the surface of the water. This is a good thing.

That scum means that it’s getting to work removing all that nasty biofilm from the pipes. You’ll be draining the hot tub afterward, so there’s no need to worry.

Drain the water

With the plumbing now free of biofilm and sparkling clean, it’s time to drain all that yucky water.

For safety reasons, you must cut all power by flipping the breaker switch and unplugging the hot tub before draining the water to avoid any risk of electrocution.

Draining a hot tub takes quite some time, which is why I decided to get myself a submersible pumpOpens in a new tab.. It turns a job that would ordinarily take hours into minutes.

If you don’t own a sump pump, then connect your garden hose to the spa drain and let gravity do its thing.

The water must be drained into the sewer system. Never dispose of hot tub water into a storm drain as they lead to natural bodies of water and can harm fish and wildlife.

Clean the hot tub shell

For best results, use this specially formulated hot tub surface cleanerOpens in a new tab.. It comes in a handy spray bottle to make application a lot easier.

Spray the shell thoroughly, paying attention to any nooks and crannies where bacteria could be hiding. Allow the cleaner to work for 15 minutes.

Now use a soft microfiber clothOpens in a new tab. or non-scratch spongeOpens in a new tab. scrubber to remove the chemical residue.

Rinse the hot tub shell thoroughly. If you don’t get rid of all the chemical residue, you might cause foaming after you refill with fresh water.

Ensure that all the jets are open once you’ve finished cleaning to reduce the risk of water pressure problems caused by trapped air.

Remove all wastewater

You’ll now need to drain the rinse water from the hot tub by connecting the hose to the spa drain.

There’ll be an inch or two of water sitting in the footwells after draining. Some hot tub owners choose to fill up their spa without bothering to get rid of that last bit of water.

But now more than ever, should you take the time to get rid of every last drop. The last thing you want is for any biofilm or chemical cleaner to contaminate the fresh, new water.

There are two ways to dry the spa shell: the easy way and the hard way. As I like to make life as easy as possible, I use a wet/dry vacOpens in a new tab.. It’s so much quicker and less exhausting than doing it by hand.

But you can always use the soft microfiber cloths to soak up all the remaining water. Just make sure it’s completely dry and sparkling clean.

Refill with fresh water

Water and electricity do not mix. Before you add fresh water, check that the breaker switch is still off.

Make sure that you’ve closed the spa drain before you begin refilling. Now it’s time to refill with fresh, clean water from your garden hose.

Your hose should have a inline pre-filterOpens in a new tab. attached to filter out the impurities that can affect your water chemistry.

They’re inexpensive and pay for themselves by you not having to add so many chemicals later on trying to balance the water. They also reduce the risk of mineral deposit build-up and staining.

Place the hose inside the filter well to prevent airlocks and begin refilling.

How to prevent hot tub biofilm

You can prevent biofilm by maintaining a regular cleaning and sanitizing schedule. It’s far better to be proactive with maintenance to prevent a build-up that requires a lot more work to remove.

Balance the water

Test and adjust the pH and alkalinity levels in your spa water once a week. Sanitizing chemicals do not work properly when the water is not balanced properly, which leads to the formation of biofilm.

Balance the alkalinity first before moving on to the pH. The total alkalinity levels should be between 80 to 120 ppm.

Optimum pH levels are between 7.4 and 7.6, but a range of 7.2 to 7.8 is still acceptable and safe. This bundle has all the chemicalsOpens in a new tab. needed to balance the alkalinity and pH.

Shock regularly

Shocking your hot tub water on a weekly basis prevents bacteria and microorganisms from building up in the plumbing.

If you use bromineOpens in a new tab. as your sanitizer of choice, then adding shock once a week reactivates the bromides to keep your water safe and clean.

A good idea to prevent a build-up of biofilm is to add non-chlorine shockOpens in a new tab. after each use to help your sanitizer work more efficiently.

Non-chlorine shock rapidly oxidizes any organic matter that has been introduced to the water, helping to keep the water clearer for longer.

Clean the filters

Maintaining your filters is essential for water clarity. The filters should be rinsed with fresh water on a weekly basis, rinsed with chemicals on a monthly basis, and placed in a chemical soak every three months.

Check out my guide for more information on how to properly maintain your spa filter, along with how to identify when it’s time to replace it.

Keep the water circulating

Ensure that the water is circulating around the hot tub when it’s not in use to prevent stagnation. Leaving the jets open also allows the water to flow continuously.

Keep your hot tub covered

Using an insulated cover when the spa is not in use prevents dirt and debris from entering the water, causing it to become unbalanced.

If the cover has become waterlogged or contains cracks, then make sure to replace it as soon as possible to avoid any contaminants from dripping into the water.

For extra protection, I like to combine my insulated cover with a floating thermal blanketOpens in a new tab.. It prevents up to 95% evaporation, which means that the water stays fresh by not losing sanitizing chemicals to the air.

Floating blankets have many benefits besides stopping evaporation, which will make you wonder why you didn’t buy one sooner.

Drain and clean every quarter

The best way to get rid of any biofilm build-up in the plumbing is to use a line flush each time before you drain the hot tub.

This way, you can be sure that there’s nothing lurking inside the plumbing that could contaminate the next batch of water.

It’s essential to drain all of the water in your hot tub every 3-4 months. If your spa sees heavy use, then you may even need to drain it more frequently.

There comes a time when the water can no longer tolerate more chemicals, rendering them useless. When this happens, you’re at risk of a biofilm build-up.

Draining the hot tub water enables you to start over afresh, and allows you to give the hot tub shell a thorough clean.

Partial drains are a good idea if the hot tub has seen a lot of use over a short period of time, perhaps because of a party or other social gathering.

Clean your hot tub shell

Between quarterly drains, it’s worth using a melamine spongeOpens in a new tab. (also known as a Magic Eraser) to clean the hot tub shell above the waterline.

If you were to use vinegar or chemicals to clean the shell, you run the risk of throwing the water out of balance as they seep into the water. Melamine sponges allow you to clean around the edge without the risk.

Always clean your hot tub shell thoroughly between drains. This can be done with a special hot tub surface cleaner or using diluted bleach.

Rinse thoroughly and remove all wastewater with a wet/dry vac or by hand. Don’t run the risk of filling up with fresh water without first drying the footwells and any other places containing wastewater.

Joshua Milton

Joshua Milton is a seasoned hot tub enthusiast. With many years of experience in the industry, he offers valuable insights on hot tub maintenance, health benefits, and relaxation techniques.

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