Oily Scum in Your Hot Tub

An oily residue floating on the surface or around the rim of your spa is not only unsightly, it’s also a wonderful environment for microorganisms to thrive and contaminate your water. There are several reasons you may be encountering this grimy film in your haven: personal care products, sanitizer or chemical imbalance, filter problems, or impurities in the water. As with any issue in your spa, trying to determine the cause can be tricky, however there are some clues that can help you to figure out the root of your oily grimy mess.


The colour of the scum is a good indicator as to what is causing the problem and what steps to take to eliminate it from your spa:

  • If the water chemical ratio is off in your hot tub you can encounter a brown scum on the sides and in the water. This occurs when the pH levels are too high, causing partials such as iron to react with the water. To correct the pH levels adding a product like pH decreaser or increaser as needed should bring the pH back to a normal range.
  • A green scum in your spa shows there are metals present in the water. Dissolved metals can interact with your sanitizer leaving behind green scum; the most common are copper and magnesium. Filter the water using a hose pre-filter as you fill or add water to your hot tub if this is a common problem for you.
  • Blue-green scum is another colour you may happen upon and is usually an indicator that the filter is dirty or clogged. The combination for body oils, personal care products and particles dissolved in the water get stuck in the filter and when the filter is not cleaned regularly it will leave a blue-green scum in the water. If you notice this colour, give your filter a thorough check and clean it by rinsing with your hose or soaking it in filter cleaner.


Some simple steps you can take to rid your backyard retreat of oily grime:

  • Grab your spa skimmer and skim off as much of the gunk from the surface as you can.
  • Check your filters, giving them a good clean or even replacing them, if necessary. Having 2 sets of filters is not a bad idea, this will allow you to clean or soak the filter while still enjoying your spa. 
  • If it appears your scum is from from a mineral buildup, a scale prevention product will soften the water and help to prevent metals such as copper and iron from building up in the water.
  • Floating sponges are another helpful tool for collecting the body oils and lotions that build up, they help to stop oil and grease from entering your filtration system or disrupting your chemical balance.
  • A water clarifier or shock once a week will break down organic matter left over from our bodies, keeping water clear and allowing it to be removed by the hot tub filtration system.


Keeping your water chemicals balanced is the solution for many spa hiccups and scum is no different. Doing regular water tests to ensure sanitizer, pH and alkalinity are correct will keep your spa water healthy and ensure oil and grime don't overwhelm the system. Keeping up with a hot tub cleaning routine is also a great preventative measure, doing regular complete water drains, flushing the plumbing and jets and giving the inside a good scrub will definitely help you avoid a gross grimy tub.


Shocking your hot tub once a week to eliminate dissolved oils and biologic material, will help with sanitizer levels and fight oily scum. The final step to avoid gunk in your beautiful spa is a quick rinse. Most oily scum is caused by oil, soaps and other personal care products we put on our bodies, removing them before a dip is the simplest way to prevent contaminating your water.


Oily, greasy scum is a common problem that most spa owners will experience during the lifetime of their hot tub. Remember, though there are a few different reasons for grime in your spa, most scum is caused by us. A quick rinse is a great first step to keeping your water clean, clear and scum free. Along with good water maintenance and hot tub upkeep you shouldn't have to worry about gross, unsightly scum again.