Why is My Pool Foamy? | Splash Mob Pools

You walk out to your pool and see foam on the surface — clusters of bubbles that don’t pop, maybe a frothy buildup near the return jets or waterfall. Pool foam is a common issue, and while it’s rarely dangerous, it signals something in the water that shouldn’t be there. Understanding the cause determines the fix.

What Causes Pool Foam?

Foam in a pool forms when surfactants — compounds that reduce surface tension — are present in the water. Normal pool water has high surface tension, which means air bubbles pop quickly. When surfactants are introduced, those bubbles stabilize and accumulate as visible foam.

The most common sources:

1. Algaecide (Quaternary Ammonium Compounds)

This is the number one cause of foamy pools. Many popular algaecides — particularly the inexpensive “quat” (quaternary ammonium) formulas — are essentially surfactants. They work by disrupting algae cell walls, but they also reduce water surface tension.

How it happens:

Adding too much algaecide at once
Using a quat-based algaecide in a pool with a waterfall, fountain, or spa jets (the agitation creates foam from the surfactant)
Accumulation from repeated algaecide doses without adequate water replacement

The fix: Stop adding algaecide. The foam will dissipate over several days as the surfactant breaks down and is filtered out. Running the pump continuously speeds this up. For severe foaming, a partial water replacement (10–15% drain and refill) dilutes the concentration faster.

Prevention: Use a poly-based (polyquat 60) algaecide instead of a quat-based formula. Polyquat algaecides are non-foaming and more effective per dose. They cost more but avoid the foam problem entirely.

2. Body Oils, Lotions, and Sunscreen

Swimmers introduce a surprising amount of organic material into pool water:

Sunscreen (especially waterproof formulas with oils and silicones)
Body lotions and moisturizers
Hair products (conditioner, gel, spray)
Deodorant
Natural body oils and sweat

When multiple swimmers use the pool — especially without showering first — these products accumulate in the water. Return jets and water features then agitate the water, creating foam from the suspended oils and surfactants.

The fix: Shock the pool with a chlorine shock treatment to oxidize the organic compounds. Run the filter continuously for 24–48 hours. Clean or replace the filter if it becomes loaded with oily residue (you can often smell it on a dirty cartridge).

Prevention: Encourage swimmers to shower before entering the pool. This single habit dramatically reduces the introduction of lotions, oils, and personal care products. It’s standard practice at commercial pools for exactly this reason.

3. High Total Dissolved Solids (TDS)

As pool water ages, TDS — the cumulative concentration of all dissolved substances — increases. In Phoenix, where evaporation is extreme and minerals concentrate over time, TDS climbs steadily.

High TDS water is more prone to foaming because the dissolved solids reduce surface tension slightly. Combined with any other surfactant source, elevated TDS makes foam more likely and more persistent.

The fix: There’s no chemical that reduces TDS. The solution is a partial or full drain and refill, which resets TDS to your source water baseline (typically 500–800 ppm in the Phoenix area).

Prevention: Drain and refill your pool every 3–5 years, or when TDS exceeds 3,000 ppm.

4. Household Detergents and Soaps

Contamination from soaps or detergents is more common than most pool owners realize:

Swimsuits washed with laundry detergent and not rinsed thoroughly
Pool toys cleaned with dish soap
Cleaning products used on the pool deck that wash into the water
Kids adding soap to the pool intentionally (it happens)

Even a small amount of detergent in 15,000 gallons of water can produce visible foam, especially if the pool has active water features.

The fix: For minor contamination, running the pump and filter continuously for 24–48 hours allows the filter to capture some of the surfactant. For heavier contamination, a partial drain and refill is faster. Enzyme-based pool products can also help break down soap-based surfactants.

Prevention: Rinse swimsuits with plain water after washing. Don’t use soap-based cleaners near the pool edge. Keep household cleaning products away from pool water.

5. Low Calcium Hardness

Water with very low calcium hardness (below 150 ppm) is “soft” and has lower surface tension than properly balanced water. Soft water foams more easily from any agitation — return jets, waterfalls, and spa bubblers all become foam generators.

The fix: Test calcium hardness and raise it to the recommended range (200–400 ppm) by adding calcium chloride. This increases surface tension and reduces the tendency to foam.

Prevention: Monitor calcium hardness as part of your regular water chemistry testing. In Phoenix, calcium tends to be high rather than low in most fill water, but after a drain and refill with softened water or in pools with aggressive chemical treatment, low calcium can occur.

6. Air Leaks in the Plumbing

Not all foam is chemical. A suction-side air leak — at the pump lid, a cracked fitting, or a loose union — introduces air into the return water. This creates persistent bubbles at the return jets that can look like foam.

How to tell the difference: Chemical foam is frothy and persists on the surface. Air-leak bubbles are larger, appear directly at the return jets, and pop more readily. You may also notice the pump strainer basket isn’t staying full, or you hear a hissing sound at the equipment pad.

The fix: Inspect and tighten all suction-side fittings. Check the pump lid O-ring for wear or debris. If the leak is underground, professional leak detection is needed.

The Diagnostic Process

When you see foam, work through this sequence:

Did you recently add algaecide? If yes, that’s almost certainly the cause. Wait it out.
Was there a pool party or heavy use? Body products are likely the cause. Shock and filter.
When was the pool last drained? If TDS is high, dilution is the answer.
Could soap or detergent have entered the water? Investigate and flush.
What’s the calcium hardness? If low, raise it.
Are bubbles coming from the jets specifically? Check for an air leak.

Most foaming resolves within 24–72 hours once the cause is identified and addressed. If foam persists despite treatment, a water sample tested for surfactant contamination or TDS can narrow down the root cause.

Dealing with foamy or unusual water conditions? Contact Splash Mob Pools — we diagnose water quality issues and get your pool back to normal.