Introduction

Algae is the most common problem pool owners in Northern Virginia deal with, and it almost always comes as a surprise. The good news is algae is fixable in most cases, and once you understand why it happens you can stop it coming back.

Key Takeaways

• There are 3 main types of pool algae and each needs a different fix

• Algae grows when chlorine drops, pH drifts, or circulation slows down

• Virginia summers make algae grow faster than most owners expect

• Catching it early takes a day to fix, leaving it takes up to a week

Why Algae Grows in the First Place

Algae does not appear out of nowhere. It grows when the conditions in your pool allow it to. The most common triggers are:

• Chlorine dropping below 1 ppm for more than 24 to 48 hours

• pH climbing above 7.8, which makes chlorine far less effective

• Pump not running long enough to fully circulate the water

• Heavy rain washing in pollen, dirt, and fertiliser runoff

• Hot weather speeding up algae growth faster than chemicals keep up

Fix the conditions and you fix the algae problem long term.

1. Green Algae

Green algae is by far the most common type. If your pool has turned green, this is almost certainly what you are dealing with.

It spreads fast, especially in Virginia summer heat, and can turn a clear pool noticeably green within 48 hours if chlorine drops.

How to fix it:

• Brush all walls, steps, and corners thoroughly before adding any chemicals

• Test and adjust pH to between 7.4 and 7.6 before shocking

• Shock the pool with 2 to 3 times the normal chlorine dose, added at dusk

• Run the pump and filter continuously, 24 hours a day, until water clears

• Vacuum dead algae off the floor once it settles, usually after 24 to 48 hours

• Add an algaecide after shocking to prevent regrowth

The water will turn cloudy blue before it clears completely. That is normal. Keep the filter running and do not stop mid-treatment.

How long it takes: 2 to 4 days for a moderate bloom. Up to a week for a severe one.

2. Yellow Algae

Yellow or mustard algae is trickier than green. It looks like sand or pollen sitting on the walls and floor, and it brushes off easily, which makes people think it is not algae at all.

The problem is it comes back quickly and is more resistant to normal chlorine levels than green algae.

How to fix it:

• Brush affected areas thoroughly, it will cloud the water and that is fine

• Wash any pool toys, floats, or brushes that have been in the water, yellow algae clings to them and reintroduces itself

• Shock the pool with 3 to 4 times the normal dose

• Use a yellow algae specific algaecide alongside the shock treatment

• Run the filter continuously and clean or backwash it daily during treatment

• Brush again 24 hours later to dislodge anything still clinging to surfaces

How long it takes: 3 to 5 days with consistent treatment.

3. Black Algae

Black algae is the most serious type and the hardest to get rid of. It appears as dark spots on pool walls or floors, often in rough or porous surfaces like plaster or concrete, and it has deep roots that make it extremely resistant to standard treatment.

If you see small dark circles that do not brush off easily, that is black algae and it needs aggressive treatment.

How to fix it:

• Use a stiff wire brush directly on each spot, not a soft brush, to break through the protective layer

• Apply a black algae specific treatment or granular chlorine directly onto the spots

• Shock the pool heavily, at least 3 times the normal dose

• Run the filter 24 hours a day throughout treatment

• Repeat brushing and spot treatment every 2 days until spots are gone

• In severe cases an acid wash may be the only way to fully remove it

Black algae that keeps coming back after repeated treatment usually means it has penetrated deep into the pool surface. At that point calling a professional is the right move.

How long it takes: 1 to 2 weeks minimum. Severe cases may need professional intervention.

Quick Reference: Different Algae Types

How to Stop Algae From Coming Back

Once you have cleared it, the goal is to stop it returning. The main things that keep algae away are:

• Testing water 2 to 3 times per week and keeping chlorine between 1 and 3 ppm

• Running the pump at least 8 hours per day during summer

• Brushing walls and steps weekly, even when the water looks clean

• Testing immediately after heavy rain and adjusting chemistry the same day

• Adding a maintenance dose of algaecide weekly during peak Virginia summer

The pools that never get algae are not lucky. They are just consistent.

When to Call a Professional

Handle green algae yourself if you catch it early. Call a professional when:

• The water is dark green and you cannot see the floor at all

• You have shocked the pool twice and it is still not clearing

• You are dealing with black algae that keeps returning

• The pool cleared but turned green again within a few days

• You are not sure what type of algae you are dealing with

If you are in Northern Virginia or Washington DC and your pool has gone green, get in touch with Paradise Pool Service and we will come out, assess the situation, and get it cleared as fast as possible.