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    Swimming Pool Waterline Scum, Stain & Scale

    December 14, 2015


    Scum, Stains and Scale can build-up easily at the waterline on swimming pools. Ugly to look at, and damaging to vinyl or plaster surfaces.

    If you're like me, you'll do almost anything to remove unsightly marks on a pool, and having worked on pools most of my life, I've had the chance to try many methods of removing pool stains.

    Waterline stains can be particularly vexing however, because of their location (high on the wall), orientation (vertical) and often advanced condition (stain severity).

    There are 3 types of swimming pool water-line problems - Scum, Stains and Scale.


    Back in the 80's I was a lifeguard at local community pools. One of my daily chores was to scrub the tiles, to remove the oily scum that accumulated on the surface. The method of choice was, and still is Comet cleanser, or similar chlorine-based abrasive cleanser, and a scrub brush or scrubbing pad. Scrubbing the inside of the skimmers is also important, as I soon found out - if I just cleaned the inside of the (8) pool skimmers twice per day, with cleanser and a brush, I could avoid having to clean all of the tiles (100's!).

    super-tile-and-vinyl-cleanerFor Vinyl Pools, a chlorine cleanser is too harsh and not recommended for cleaning oily scum lines. To clean the waterline on a vinyl pool liner, use a mild Tile & Vinyl Cleaner, and never use any household (kitchen/bath) cleaner, which would not be good for your pool water.

    In the 90's Enzymes were introduced to the pool industry, as a way to control oily organics - not just for scum-line prevention, but as a way to improve overall water chemistry. Pool Enzymes consume oils and organics, actually digesting them, in the same way that enzymes are used to clean up ocean oil spills.

    pool-perfect-by-natural-chemistry-If your pool has a Scum problem, from oily pollutants that fall from the skies, or introduced by swimmers - you could benefit from regular treatment with a Pool Enzyme product like Pool Perfect, or using a Scum Ball to soak up the oils. In addition, be sure to soak cartridges or filter sand with a pool filter cleaner once per year, or replace the filter media with new, if oily conditions have existed for several years, or for a single large oil contamination.


    Waterline stains are those that won't scrub off easily, and may be below the tile line. Plaster pools that are winterized can often develop waterline stains from leaves and debris, environmental pollution or chemical imbalances, leaving blackish gray marks for the first foot below the water line.

    acid-magic-for-poolsThe quickest way to clean tile and plaster of stains is to acid wash the top part of the pool wall. Lower the water level below the lowest waterline mark in the pool, and use a flower watering can to pour a blend of muriatic acid (or Acid Magic) and water over the stain, as you walk around the edge. A solution of 1 part Acid added to 4 parts water will usually do the trick, but heavier stains will require a stronger mix. Really heavy stains will also require a helper following behind with a sturdy brush on a pole, to scrub the area quickly before rinsing. Rinse the acid off quickly and thoroughly, after about 30-45 seconds, to remove all traces of acid from the walls and steps. Afterwards, check your pH and Alkalinity levels, which will both be lower from the muriatic acid used to clean the walls.

    For Vinyl Pools, you can't go around pouring acid over vinyl, and it's not very effective anyway. The first thing to try is a Magic Eraser™, those little white sponges made by Mr. Clean™. They really work well on many vinyl stain types, above or below the water level - but you do need to put some elbow grease on them, and scrub at the vinyl stain.

    stain-free-2However, not everyone wants to drain a foot of water from their pool, and not everyone is even allowed to, in areas with water restrictions. Another options is an all-over pool chemical treatment, using Stain Free, an all natural stain remover made from ascorbic acid, so it's gentle on vinyl and fiberglass pools. For the strongest stain remover for all pool types, see the A+ Stain Remover. Note that both products recommend the use of a sequestering agent in addition to the stain remover, to lock up any metals and minerals that can be causing the waterline stains, in addition to a very low Free Chlorine level.


    In hard water areas, waterline scale is very common. Often a whitish deposit, it can mix with dirts and oils to take on a brownish or gray color. In Arizona and other areas, there are companies that specialize in bead-blasting tiles for scale removal, which can produce excellent results.

    Calcium scale, or efflorescence can also be scraped off with a putty knife, or flat head screwdriver, and then polished up with a muriatic acid solution. Acid can be poured on, or if you have a clean spray bottle, fill it half full of water, then add acid to fill the bottle. Now you can spray on just enough acid to do the job, with less effect on your pool pH. Be sure to wear gloves and goggles, and rinse off the acid within a minute of being on the tile, so it won't etch into the tile grout too much. You can also remove scale with a nylon wire wheel or Drill Brush™ on a cordless drill.

    For Vinyl Pools, you should probably avoid using grinding wheels or muriatic acid to remove calcium deposits. Some say that Calcium won't stick to vinyl, but it can - I've seen it many times. What we started doing about ten years ago is dissolving a cup of Stain Free (the Vitamin C powder) into a spray bottle, to spray vinyl liner water line scale. If your liner has a whitish layer around the waterline, you can actually use a mild acid (like vinegar or ascorbic acid) to test a small area for successful scale removal.

    mr-clean-magic-eraserThe Magic Eraser is also useful for scale, if deposits are thin; but when they are built up over several years, or for very hard water pools with deposits over the entire pool surface, you'll be better off using Stain Free or A+ Stain Remover, in combination with a sequestering agent (like Metal Free or Stain Away).

    Scale forms from high levels of calcium and other minerals coming out of solution. Sequestering agents keep minerals and metals locked up - in solution, where they can't deposit themselves onto the pool surfaces.

    I hope that this has been helpful for you! If you're still confused or want to talk to someone about your waterline pool stains, give us a call, perhaps sending a picture or two along with a history of the stain, and we'll help you create a sensible plan for stain removal.

    After all - pool stains are not new, and there will always be pool owners who can't stand to look at pool stains - like me!  

    Sheryl Somers
    SPP Pool Expert  

    Blog Author
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