Slideshow: A Defense Against Stains

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See how pros apply Stain Barrier to prevent organic matter from seeping through.

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The rookie on the crew pulled back the liner, revealing a Rorschach test of black and pink splotches that spread across the floor like an oil slick. He placed a hand on the slimy surface, causing the site superintendent to gasp. “That’s radioactive algae!” The panicked apprentice fled to wash off the toxic sludge, but the ensuing eruption of laughter suggested that he’d been had. He’d have a hard time living that one down.

“I happened to be there that day, and it was so funny,” recalls Frank Christiana, owner of The Liner Specialists in Carmel, N.Y.

All pranking aside, the horrors that lurk under liners are no laughing matter. They can cause homeowners and service technicians no end of torment. Here, we’ll explore what it takes to vanquish underside stains the moment they rear their ugly heads.

From the ground up

It’s strange to think that a 20- to 30-mil liner can retain tens of thousands of gallons of water, but can’t prevent something seeping through from the other side.

What’s leeching through isn’t mere algae. It’s something far more menacing: Bacteria, mold or fungus. “What differentiates it from algae is that it’s more of a parasitic-type organism,” says Terry Arko, water specialist for SeaKlear Pool & Spa Products, based in Bothell, Wash.

These micro-organisms develop colonies behind the liner and, left unchecked, eventually will permeate through to the printed side, appearing as dark gray or black splotches. To prevent this, many manufacturers incorporate biocides within the makeup of the vinyl, but this isn’t always a bulletproof solution.

This sort of stain often is misdiagnosed as black algae, Arko says. Treating it as such, many technicians drop the pH and super chlorinate the water. Some will even dive down to scrub off the stain with a chlorine tab inside a sock.

The stain will fade. But don’t expect longterm results. While high doses of sanitizer will keep subsurface stains at bay, they will return once chlorine levels drop.

Sometimes this is the only way to know for certain that something is festering on the backside of the liner.

Other times, the surrounding environment offers clues that the source of the problem may lurk in the ground. For instance, skunk cabbage raises Christiana’s suspicions. This wetland-thriving, foul-smelling plant can suggest there may be nasty things below the pool.

“When I see a low-lying, boggy area with skunk cabbage growing, then right away my thought process goes to the possibility of [fungus] growing, because it is damp under the pool,” Christiana says.

The stains often are found on the deep end, where the vessel is more likely to encounter groundwater that harbors contaminants. Even after this groundwater recedes, bacteria and mold remain.

Sand-bottom shells are especially susceptible to spoilage, but vermiculite isn’t immune. In extreme cases, stains may creep up the walls.

Some theorize that the ground may be contaminated with septic runoff.

“I’ve heard it really becomes a blatant problem where there is sewage water leaking into the ground beneath the liner,” says Steve White, president of Underwater Pool Masters in West Boylston, Mass.

White uses his diving expertise to analyze stubborn stains. A close inspection will reveal when the blotching occurs from behind, he says.

Breaking the mold

When faced with this reality, a tech has several options.

Some professionals claim that the most effective defense against spoilage is to place a barrier between the liner and the ground.

Christiana has had tremendous success with Stain Barrier from Tara Manufacturing. It rolls on like paint. It’s recommended for vermiculite bottoms only.

Though the product creates a layer of protection between the liner and creeping crud, as a precaution you may want to chunk out some of the most affected parts of the vermiculite floor and patch the holes with new material, Christiana advises.

Give the shell adequate time to dry, remove all debris and patch all cracks before applying the latex coating.

Apply the barrier to the entire surface, or you could leave the pool vulnerable to more blemishing.

“What if we’re fighting the stain over here and it migrates over there?” Christiana cautions. “I haven’t taken that chance.”

Give the shell at least 24 hours to dry before replacing the liner.

I’ve heard it really becomes a blatant problem where there is sewage water leaking into the ground beneath the liner.

Beyond a roll-on barrier, there is another method for keeping micro-organisms in their place. Installing a polyethylene sheet behind the liner inhibits bacteria from spreading to the surface. While effective, it does present a potential drawback: If the liner floats, the plastic layer under it could wrinkle.

In less extreme cases, a little bleach might eradicate the problem. After giving the shell time to air out, the stains may flake off with a stiff bristled brush. Then treat the floor and walls chemically with a solution of water and bleach.

Repeat this several times.

Be sure to apply the mixture to the underside of the liner, as well.

Spraying the floor with a water/bleach solution may be your only option with a sand-bottom floor. This will help destroy bacteria and fungus and prevent further growth. However, you may consider replacing the sand altogether if it appears extremely spoiled.

Is the liner a goner?

After hearing the treatment options available to them, clients will want to know first and foremost whether the existing liner must be replaced.

That, of course, depends on its condition before being removed. “Sometimes the liner is salvageable, if it’s relatively new,” Christiana says.

In that case, customers only pay for the water, treatment product and labor.

Provided the liner fit properly to begin with, it can be reset, though Christiana concedes that’s not always a possibility. “Some of my competitors make it extremely tight, but I can evaluate it,” he says.

The homeowners also must decide whether they are willing to live with the stain. Even though the problem’s source has been eradicated, the surface stain may never go away entirely.

If they decide to replace the liner, Christiana advises going with a darker pattern. That way, in the unlikely case that the blemish returns, it will blend in.

The no-drain approach

The problem with the above solutions is that they require removing the liner — a labor expense not all customers will pay.

In such cases, a couple possibilities deserve exploration. Some have had good results sprinkling fungicide around the pool to quell the spread of fungus and bacteria. The chemical is fairly inexpensive and can be found at most agricultural suppliers.

Begin by digging a trench 3 inches deep at the edge of the decking around the pool. Pour evenly throughout the trench. Instruct the homeowner to soak the trench with a hose for two or three days so the chemical can work its way into the ground.

Of course, this is not a guaranteed cure.

“I’ve heard of cases where it’s worked and I’ve heard of cases where it hasn’t worked,” Arko says.

This might serve better as a preventive measure, he says, but it’s worth a shot.

When all else fails, you may have to dive down and stab the stains with a syringe full of sodium hypochlorite.

White, the Massachusetts diver, has only tried this technique with sand-bottom pools, which are more easily punctured with a needle. However, he believes it would work equally well on vermiculite. He’d simply have to inject at an angle.

Of course, the liner will need patching. Fortunately, clear underwater patching kits are available.

This is almost always a last-ditch effort. No one likes the idea of poking holes in vinyl. And it may require a lot of holes.

“I would hate to have to do that on a new liner,” White says.