The black stuff on your pool deck in Florida is usually algae, mold, and mildew. These grow on any deck that stays damp, and a pool deck is damp most of the year. So the real fix is to kill the growth and then keep the deck drier.
At Top Down Exterior Cleaning, we have cleaned pool decks around Lakeland since 2010. As a result, we see these black spots all over Polk County. Below, we explain what they are, why they showed up, and how to clear them safely.
Is the Black Stuff on My Pool Deck Mold, Mildew, or Algae?
Most of the time, it is all three living together. However, a few dark marks on a pool deck are plain stains. Here is how to tell what you have:
- Black spots and gray patches. These are usually mold and mildew. They start in corners and spread outward.
- A dark or green slick film. This is algae. It feels slimy under bare feet.
- Brown or black leaf shapes. These are stains from wet leaves. They do not feel slick.
- Dark, greasy areas by the chairs. These often come from sunscreen, pool chemicals, and dirt.
Here is a simple check. Wet the spot with a hose and look at how it sits. Growth looks darker and feels slippery when wet. A stain looks the same and feels like the rest of the deck.
Does Black Stuff on the Pool Deck Mean My Pool Water Is Bad?
No, black stuff on the deck does not mean your pool water is off. Deck growth comes from moisture and shade on the surface around the pool. Black algae inside the pool is a separate problem, and your pool service handles that one.
However, the two can show up at the same time. So if you see dark spots on the pool walls too, mention it to your pool tech. We clean the deck, and they treat the water.
Why Does Black Stuff Grow on Pool Decks in Florida?
Black stuff grows on pool decks because the surface almost never dries out. Splash-out, sprinkler spray, and Florida humidity keep the deck wet nearly all year. Then shade from the screen cage, the house, and nearby plants slows the drying even more.
Garden experts say the same thing. For example, the Royal Horticultural Society notes that algae thrive in wet conditions. It also says growth may be faster in shady spots with poor airflow. A screened pool deck checks every one of those boxes.
So the black usually shows up in the same places first:
- Along the wall of the house, where the sun rarely reaches
- Under planters, chairs, and grill mats
- In low spots where water puddles
- Around the coping and the steps
- In the joints between pavers
Is the Black Stuff on My Pool Deck Dangerous?
The biggest danger is a fall. Algae and mildew turn slick when wet, and a pool deck is where people walk barefoot and kids run. Therefore, a black or green deck is a real slip hazard.
The growth itself will not eat through your concrete. Still, it should not sit there. It spreads, the stains set deeper, and the deck looks older than it is. Also, a wet film tracks into the pool and the house on every foot.
How Do You Get the Black Stuff Off a Pool Deck Safely?
You get the black stuff off a pool deck by killing the growth first and then rinsing it away. Water alone only knocks off the top layer. So the black comes right back.
Our pool deck cleaning in Lakeland, FL follows three simple steps:
- First, we match the method to your deck. Brushed concrete, pavers, travertine, and coated decks each need a different cleaner and pressure.
- Next, we treat the growth. The cleaner goes after algae, mold, and mildew at the root.
- Then, we rinse. We wash away the residue and leave a clean surface with better grip.
We also protect your pool. We direct water away from the edge, and we rinse carefully along the coping. That keeps runoff out of the water.
Can You Pressure Wash the Black Stuff Off a Pool Deck Yourself?
You can, but a rental machine makes it easy to use too much pressure. Too much pressure can etch concrete and strip a deck coating. It can also blow the sand out of paver joints.
On top of that, a narrow tip leaves stripes that show every time the deck gets wet. So if you try it, start low and test a hidden corner first.
How Do You Keep the Black Stuff From Coming Back on Your Pool Deck?
You keep the black stuff away by helping your deck dry faster. No cleaning lasts forever in Florida. However, these habits slow the growth down:
- Move things around. Shift planters, mats, and chairs so the deck under them can dry.
- Aim your sprinklers. Keep the spray off the deck and the screen.
- Clear leaves fast. Wet leaves stain the deck and feed growth.
- Fix puddles. Push standing water off with a broom after a storm.
- Trim plants back. More sun and air mean a drier deck.
Most Lakeland pool decks need a professional cleaning once or twice a year. Do you have a paver deck? Then sealing after the cleaning is a smart next step. Our paver sealing locks in the joint sand and helps the deck resist new algae and stains.
Ready to Get the Black Stuff Off Your Pool Deck?
You don’t have to tiptoe around your own pool. Top Down is family owned and insured, and we have served Lakeland since 2010. We have also earned the Angie’s List Super Service Award five times.
Contact Top Down Exterior Cleaning today for a free estimate. You can also call us at (863) 904-8956. We will come out, look at your pool deck, and give you a clear price.
