Stain Prevention with Dr. Pool

Stain Prevention with Dr. Pool

Hello, I’m Dr. Pool, and today’s class will focus on the prevention of stains, on inground pool plaster surfaces. It’s a topic that has all the elements of a good chemical story, with great play between the main characters – a semi-porous cementitious surface, 1000’s of charged particles, and of course, water.

Let’s start with pool plaster itself, typically a mixture of white Portland cement and marble dust. Mixed with water and applied by hand in uncontrolled (outdoor) conditions, it cures underwater, with proper chemical management.

Pool Plaster is a natural product, and as such is subject to variations in shading or hue, some undulations or streaking may be expected on troweled plaster. Most pool plaster companies offer additives, such as quartz, bead or pebble aggregates, added to diffuse color and hide such variations.

I say all this to help you manage expectations, as 95% of plaster pools have some uneven tones. And in addition, most pools have a blemish here or there – pool stains are normal, or the rule rather than the exception.

Nevertheless, you’ve come here to learn about preventing pool stains? read on…


Pool stains are often simply Mineral Scale. Pool Plaster has an ionic charge that attracts mineral scale, and nearly every inground plaster pool has a film of scale deposited on the surface. This is more pronounced on colored pools (blue, black or grey), and may not be noticeable on white plaster finishes.

But scale does not deposit alone, when minerals are knocked-out or pulled-out of solution, as happens quite regularly in pools – dirt, algae and organics is drawn into the forming scale, producing a dull or dirty scale film on the plaster surface, in a very thin layer.

Scale deposits and mineral stains can be avoided in pools!

Pool Filters: Large and effective, DE filters are the most efficient.

Pool Cleaners: Automatic pool cleaners run daily help reduce scale formation. ( Although you can not use one of these types of vacuums for at least 2 weeks after having your pool resurfaced ).

Brushing: Weekly brushing with a quality pool brush to loosen scale and dust.

Stain & Scale: Agents like Scale Tec or Stain Away keep minerals in solution.

Saturation Index: Avoids super-saturation or scaling conditions by referring to an LSI Calculator.

Over time, even well maintained pools can have situations that produce sudden scaling conditions. An acid wash every 5 or 10 years will strip scale film to restore and brighten plaster beneath. As an added benefit, replacing (old) pool water improves water conditions, often making water balance and scale management easier.

Scale Films and crystal deposits can also often be removed without draining the pool, albeit less effectively, by balancing the water towards the slightly acidic end of the LSI spectrum, and adding a full dose of Scale Tec or Super Stain Away directly to the water, followed by heavy brushing and extra filtering, which may be aided with Chitin, a natural clarifier.


Plaster pools can also be subject to staining from metals, the most common elements found in pool water are Copper and Iron. Iron stains produce mostly orange-brown stains and copper stains are usually blue-green, and both can appear black in high concentrations.

Metal levels in pool water can be tested for at very accurate levels ‘out in the field’, there is a Copper test strip by AquaChek, and there are strips also available for establishing a rough measure of iron, in the familiar parts per million scale.

Metals in pool water can come from many sources:

Well Water usually contains iron, or city water delivered via rusty iron pipes.

Copper from copper pipes, copper heat exchangers, or copper algaecides.

Steel: Non-pool toys with metal parts, hair pins i.e. ‘bobby pins’, roofing nails.

Rebar tie wires, close to the surface, beneath the plaster, rusting through.

Galvanic corrosion of steel in salt water pools without a zinc anode.

Metal stains from iron and copper can be prevented in pools!

Pre-Filter: Use a Pre-Filter to remove metals from pool re-fill water.

Sequester: Use Metal Free to keep metals locked in solution with strong bonds.

Proper pH & Alk: Acidic Low pH & Alkalinity strips copper from pool heaters, this is why here at Advanced Pool & Spas we recommend disconnecting your heater when having a new surface applied to prevent copper staining.

Perhaps it may also be wise to install a new pool rule – ‘no ferrous metals’ in the pool. Only aluminum, brass or stainless steel within 50 feet of the pool!

Copper and Silver ionizers can also easily stain plaster pools. Products such as the Solar Ionizer or Power Ionizer have the potential for increasing metal levels to a range where sequestration becomes difficult. A sudden change in water balance, including shocking the pool can precipitate the metals, staining a plaster surface.


Now class I ask you; is your pool stain an animal, mineral or vegetable? So far, we’ve covered mineral scale stains, and metal stains, now we look at organic stains, those from animals (birds, worms, insects) or vegetable (algae, leaves, dirt, oils).

These stains can be in the corners of the steps, or one end of the pool, around the drain, or at the winter water level line – known as the ‘bathtub ring’. Or when leaves and worms mix and sit all winter long directly on the pool plaster.

Many automatic pool cleaners have a particular spot or step that they can’t reach, and leaf tannins and oils from debris can leave a mark. Organic stains can also occur from bird droppings, or berries and nuts.

Organic Stains in pools can be prevented! (sometimes)

Solid Covers: A tight fitting fully-Solid winter safety cover without drain panels.

Enzymes: For winter or summer, Enzymes eat stain causing organics!

Clean Pools: Efficient skimmers, automatic cleaners, good cleaning tools.

Pool Filters: Operating effectively to remove fine organic particles and oils.

Sanitizer: Constant consistent chlorine levels helps to breakdown organics.

Organic stains can often be removed quickly on a plaster pool by sprinkling calcium hypochlorite (pool shock) over the area, allowing to sit for a minute, then brush briskly with a nylon brush.

Today’s lesson however, was Stain Prevention in a Plaster Pool, (not removal) and I hope you found it of value.

For those students who have passed the test on preventing pool stains, you are ready to move onto the next chapter: removing pool stains. Your next reading assignment will be thus: Stain Removal in a Plaster Pool

Class Dismissed!

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