You wake up to a gorgeous Saturday morning in Las Vegas, eager to relax in your backyard paradise. You step out, prepared for a swim, but instead of that blue glittering water you crave, your pool looks… off. Perhaps it’s green, cloudy, or even brown. Frustrating, isn’t it?

The truth is that the color of your pool conveys a statement. Different colors indicate different things, ranging from basic chemistry imbalances to larger issues such as algae or debris.

In this article, we’ll explain what each pool color represents, why it happens, and the exact steps to fix it. There’s no guesswork, just clear answers to return your water to sparkling blue.

Why is a swimming pool blue?

Short answer: light and chemistry. Longer red wavelengths are absorbed by water, and shorter blue wavelengths are scattered — that’s why clean, deep water appears blue. Your pool finish (white plaster, blue tile, or reflective glass) and the color of the sky also affect how blue your pool will appear. So when you wonder “Why is a swimming pool blue?”, keep in mind it’s both physics and aesthetics: clean water + light = pleasing blue.

If your pool is clear and the bottom is visible, that rich blue is a good sign. If it’s a weird blue-gray or tinged with green, that tells a different story (keep reading).

Common pool water colors: what they mean & what to do

Through the years, we’ve had service calls with nearly every color of the rainbow involved. Your pool changing colors can tell us precisely what’s amiss and how to correct it. Let’s dissect what’s really happening when your pool insists on changing colors.

Green Water: The Most Common Culprit

Green is by far the most common problem with swimming pool water color we see. We would say approximately 60% of our emergency service calls in the Las Vegas summer months are some variation of green water.

Light Green Water: More often than not, this means early algae growth or oxidation of copper. If you caught it in time, you’re lucky – this is pretty simple to correct with good shocking and filtration.

Dark Swamp Green: This is advanced algae territory. When your pool resembles a horror film, you’re working with a full-blown algae bloom that’s been building for days or weeks.

The tricky thing about green pool water colors is that there are actually two different causes:

Algae Growth: Usually happens when chlorine levels drop below 1 ppm or pH rises above 7.8
Copper Oxidation: Occurs when copper-based algaecides or corroding equipment introduce metals into the water

We can distinguish by checking the water chemistry. Algae-green water will register low or zero chlorine, whereas copper-green water tends to have reasonable sanitizer levels.

Brown Water: When Your Pool Looks Like Chocolate Milk

Brown pool water color is nearly always a sign of iron contamination. Here in Las Vegas, this occurs more often in homes that use well water or older homes with iron pipes.

We’ve had iron as high as 3-4 ppm in certain pools, and that produces that characteristic rust color. The horrifying part? Iron contamination can permanently stain your pool surfaces if it’s not dealt with immediately. Those brownish-red spots on your pool walls aren’t only aesthetically displeasing – they can be expensive to remove.

What causes iron problems:

Well water with naturally high iron content
Corroding pool equipment (heaters, heat exchangers, metal fittings)
pH levels below 7.0, which makes metals more soluble
Old galvanized pipes in your pool’s plumbing system

Black Water: The Nightmare Scenario

Black pool water hues are uncommon, but if they do occur, they’re severe. We most often experience this with silver contamination from ionizer systems or some sanitizing gear.

Black water is not only unpleasant – it can actually be a health hazard and result in permanent discoloration of pool surfaces. The good news is that it’s often avoidable with good equipment maintenance and water testing.

Purple Water: The Mysterious Shade

Purple may be the strangest -colored swimming pool water we’ve seen. It usually signifies manganese or magnesium contamination, which quite commonly occurs shortly after chlorination of stagnant water.

We received a service call where a homeowner came home from a two-week vacation to discover that their pool was suddenly bright purple overnight. What had caused this bizarre phenomenon? An automatic chlorinator malfunction had released a huge dose of chlorine into their well water-derived high-manganese water.

Cloudy Water: Not a Color, But Just as Important

Although cloudiness is not actually a swimming pool water colour, it’s one of the most prevalent water quality complaints we encounter. Roughly 40% of our regular service calls are some sort of water clarity issues.

Cloudy water can indicate:

Poor filtration (clogged or old filters)
Chemical imbalance (usually high pH or low chlorine)
High Total Dissolved Solids (TDS) from evaporation
Algae in very early stages

The Health Implications: Why Pool Water Colors Matter

Various colours of pool water don’t merely appear unpleasant – they can even affect your health and safety. Here’s what we’ve discovered from decades of water testing and treating:

Green Water Health Risks:

Algae can harbor harmful bacteria like E. coli and Cryptosporidium
Reduces visibility, increasing drowning risk
Can cause skin and eye irritation
Makes it impossible to see swimmers in distress

Brown Water Concerns:

Iron can stain clothing and cause hair discoloration
High iron levels may indicate other heavy metal contamination
Can interfere with chlorine effectiveness

Black/Purple Water Dangers:

Often indicates metal contamination that can be toxic
Can cause severe skin and eye irritation
May damage pool equipment and surfaces

Diagnosing Your Pool’s Color Problem: The Nationwide Pool Approach

When customers call us about unusual swimming pool water colour, here’s our systematic approach to diagnosis:

Step 1: Visual Assessment We examine the water under different lighting conditions and note any patterns (is the discoloration uniform or patchy?).

Step 2: Chemical Testing Complete water analysis, including:

Free and total chlorine
pH and alkalinity
Calcium hardness
Cyanuric acid
Metals testing (copper, iron, manganese)

Step 3: Equipment Inspection. We check all pool equipment for signs of corrosion, wear, or malfunction that could be introducing contaminants.

Step 4: Historical Analysis Understanding recent pool maintenance, chemical additions, and environmental factors helps pinpoint the cause.

What to test and target numbers

If you want to read your pool like a pro, here are the basic tests and targets:

Free Chlorine: 1–3 ppm (2–4 ppm for heavy use; 5–10 ppm when shocking)
pH: 7.2–7.6 (ideal 7.4–7.6)
Total Alkalinity: 80–120 ppm
Calcium Hardness: 200–400 ppm (helps avoid scale or corrosive water)
Cyanuric Acid (CYA): 30–50 ppm for outdoor chlorine pools
Phosphates: Keep low—high phosphate feeds algae

Test kits: use a liquid test kit or a reliable digital reader; strips are OK for weekly checks but less precise for troubleshooting.

Fixing Pool Water Colors: Solutions That Actually Work

The treatment approach depends entirely on what’s causing the discoloration. Here’s what we typically recommend:

For Green Water (Algae):

Shock Treatment: 2-3 times the normal chlorine dose
Brush Thoroughly: Physical removal is crucial
Run Filter Continuously: Until water clears completely
Maintain 5-10 ppm Chlorine: Until algae is completely gone

For Green Water (Copper):

Metal Sequestrant: Binds copper to prevent further oxidation
pH Adjustment: Raise pH to 7.6-7.8 to reduce copper solubility
Filtration: Extended runtime to remove sequestered metals

For Brown Water (Iron):

Metal Sequestrant: Different formula than copper treatment
Shock with Non-Chlorine Oxidizer: Avoids further iron oxidation
Filter Replacement: Iron particles can clog filters quickly

For Cloudy Water:

Clarifier or Flocculant: Helps particles bind together
Filter Deep Clean: Often requires professional cleaning
Water Balance Correction: Address underlying chemical issues

Fast fixes & prevention: an actionable checklist

After 40+ years in the pool business, we’ve learned that prevention is always easier and cheaper than treatment. If your pool color is off, here’s a quick plan:

Test water immediately (pH and free chlorine first).
Balance pH and alkalinity — gets chlorine working properly.
Shock if chlorine is low or if you see algae/cloudiness.
Run filter continuously until water clears; backwash or clean cartridges as needed.
Brush walls and steps daily to free algae and biofilm.
Vacuum to waste for severe algae or metal removal.
Use a sequestering agent if metals are detected.
Call pros if black algae, persistent green, or metal staining won’t respond.

Prevention tips: weekly upkeep, keep the filter cleaned, maintain chlorine and CYA levels, and cover up to minimize debris and chemical loss. In Las Vegas, where dust and heat are issues, maintaining filtration during heavy use—8–12 hours a day is a good starting point.

When to Call the Professionals

While some pool water colors can be addressed with DIY methods, certain situations require professional intervention:

Water has been discolored for more than 48 hours despite treatment attempts
You’re seeing multiple colors or rapidly changing colors
Metal staining is beginning to appear on pool surfaces
You’re uncomfortable working with pool chemicals
The problem keeps recurring despite proper maintenance

Enjoy a Clear Pool at All Times With Nationwide Pool in Las Vegas

What does pool water color be? Crystal clear with a gorgeous blue hue that makes you wanna dive right in. But when pool water colors shift, don’t panic – they’re really providing you with important information about the health of your pool.

With four decades of experience in correcting colored pools to their sparkling former selves, we can assure you that the vast majority of pool colors are entirely reversible with the proper method. The pools that consistently look wonderful are those that are serviced regularly and addressed quickly when there is a problem.

Dealing with mysterious pool water colors? Contact Nationwide Pool today for expert diagnosis and treatment. After four decades of keeping Las Vegas pools crystal clear, we know exactly what each color means and how to fix it fast.

Why Is a Swimming Pool Blue? Pool Water Colors Explained