Pool Algae in Las Vegas: Green, Yellow, and Black and How Each Is Treated

Updated 2026-11-05 · For Las Vegas pool owners

Las Vegas is an algae incubator. Water temperatures over 85 degrees from June into September, intense UV that destroys chlorine by mid-afternoon, and monsoon dust that carries spores and phosphates into the pool. A pool that would take two weeks to turn in a cooler city can go from clear to green in three days here. The color tells you which algae you have, and each one is treated differently.

What it usually means

Green algae: free-floating, clouds the water green, and wipes off walls easily. The most common type and the easiest to kill. Cause is almost always chlorine that dropped to zero.
Yellow or mustard algae: looks like pollen or sand on the shady side of the pool, the steps, and under the ladder. Brushes off but comes back in the same spot within days. It is chlorine resistant and lives on anything that touches the water, including swimsuits, floats, and pool toys.
Black algae: dark blue-black spots the size of a pencil eraser to a quarter, rooted into plaster and grout. It has a protective layer that chlorine does not penetrate, so it has to be scrubbed open first. Most common in older plaster pools and in grout lines.
Pink slime or white mold: not algae but bacteria, usually around returns and in the skimmer. Treated like green algae with high chlorine and brushing.

What a technician will check

The tech will confirm the type by rubbing a sample between gloved fingers (mustard algae smears yellow, dirt does not), test phosphates and cyanuric acid, and look at how the chlorine is being delivered. A pool with cyanuric acid above 80 or 90 ppm from years of tablets needs far more chlorine to kill algae, and a scaled salt cell may be producing almost nothing. They will also check the filter, because algae that is killed has to be filtered out, and a cartridge that is three years old will just recirculate it.

How each one is treated

Green: brush, raise chlorine to shock level and hold it there until the water clears, clean the filter daily. Two to five days. Yellow: shock at a higher level than green, add a sodium bromide or dedicated yellow algae product, brush the shady areas twice a day, and wash every float, toy, and swimsuit that has been in the pool. Then hold chlorine high for a week, because mustard algae returns if the kill is not complete. Black: break the heads open with a stainless brush or a chlorine tablet rubbed on each spot, then shock and brush daily for a week or more. Spots that are deep in the plaster may need an acid wash to remove the roots, which is a drain job.

What it costs in Las Vegas

Treatment	Las Vegas range
Green algae, chemical cleanup	$350 to $800
Yellow algae, extra visits and products	$150 to $400 on top of normal service
Black algae, scrub and treat over several visits	$300 to $800
Acid wash for rooted black algae (pool drained)	$300 to $700 plus drain and refill
Dark or black green water	$800 to $1,500 and up

These are Las Vegas ranges to judge a quote by, not a quote. The price tracks how many return visits the job needs, and black algae in grout can take four or five. If a company quotes one visit for black algae, ask what happens when it comes back.

Can you do it yourself

Green algae is a good DIY job if the pump and filter work. Yellow algae is doable but tedious, and most people give up before the week of high chlorine is over, which is why it comes back. Black algae is the one to hand off: the scrubbing is hard on the plaster, and knowing when to stop and acid wash instead is judgment a technician has. Whatever the type, the real fix is the cause: more chlorine in summer, a working filter, and a drain every three to four years to reset the stabilizer that Las Vegas water builds up.

Algae keeps coming back? Get matched with a Las Vegas company that treats it.
We introduce you to local Las Vegas pool companies. Free for homeowners.

Get matched