Black Algae & Swimming Pool Chemistry

Swimming Pool Care

Black algae can give you a real headache if not taken care of immediately. Unlike brown algae or your run-of-the-mill green algae, this little guy forms layers and each layer forms a scab. Even when you have good pool water chemistry and practice excellent swimming pool care to a "T", it still might not be enough.

You need to get right on this because this bugger, if left on its own, will eat a hole right through your concrete.

Swimming Pool Algae Prevention

Properly balancing all of your pool’s chemicals and normal swimming pool care will greatly reduce, but may not eliminate the opportunity for getting an algae swimming pool.

You can't treat brown and green algae in the same manner as black algae.

Having your swimming pool chlorine, alkalinity, and hardness adjusted correctly is very important. Remember to brush and vacuum your pool because this will reduce the dirt accumulation and algae pores from sticking to the pool’s surface.

SAFETY FIRST

It’s easier, a bit safer, lighter in weight, easier to store, and 1 pound of granular chlorine equals 1 gallon (8lbs.) of liquid.

So, What's First?

But wait!! You've read on this site to keep your pH level at 7.6-7.8. What is the deal with 7.0-7.2? Well, glad you asked, and here it goes.

I suggest you use granular pool chlorine, a.k.a. Calcium Hypochlorite, to shock your pool. This kind of pool chlorine has a pH level of 12.

Now, anything over the pH level of 8.0 and you're only using about 25% of the chlorine, which means, you've lost 75% of the active swimming pool chlorine. When you add your pool chlorine, your pH will automatically go up, so get that pH down!!

If you start the pH a bit lower, you're using more active chlorine than you would if your starting pH was a bit higher.

These simple pool tips will reduce the amount of time and headaches when dealing with black algae and get you back on the road to your great pool water maintenance.

You want to get rid of the dead algae.

So, What's Next?

I know of two ways to get rid of black algae. Some may say that a pool algaecide specifically designed for black algae in swimming pools is a waste of time and money, but I've had some success with and without using a pool algaecide.

The algaecide you want to get is expensive, but I've heard it works pretty well. It's called a "poly quat".

First is to brush the spot(s) with a heavy duty wire brush. Doing this will loosen up the algae and help the chlorine penetrate the spot.

Remember, black algae has layers so you want to get as many layers off as possible before adding the chlorine. Kinda like Shrek. Remember he had layers, like an onion?

This is for a concrete pool and not vinyl swimming pools as this may tear your vinyl liner. Next, you'll want to apply your granular chlorine, or Calcium Hypochlorite, directly onto the black algae spot. Before you begin, make sure your pH is at minimum 7.0.

If you need to drain your pool, you can get a chlorine tablet and go to work on the spot.

You have to get mean with this because it will show no mercy for you. Grind it in, so to speak. Also, take care in using direct chlorine on your vinyl liner as it may bleach or stain the vinyl liner.

Second way is to use 128oz. of granular chlorine and two gallons of ammonia hydroxide. Obviously you'll want to close the pool for at least two weeks.

This is powerful stuff and I wouldn't want anything to happen to you, your family, or pets.

Add the pool chlorine around the perimeter of the pool and allow the filtration system to run for 24 hours. Now, carefully add the ammonia hydroxide. Be sure to use safety goggles, glasses, and heavy duty rubber gloves. Again, allow your system to run for another 24 hours. Vigorously brush your pool as often as you can. You have to get that black algae up from the roots.

Allow your system to run until the chlorine is down to 1.0-3.0ppm, normally about 2 weeks, maybe even less if you have a stretch of hot days.

What this does is brings your chlorine level up to an insane amount, about 50ppm, but this is black algae we're talking about.

You're literally burning the black algae up. This isn't holding hands and skipping to Grandma's house for Sunday dinner.

Once the chlorine is down to a safe level and your swimming pool chemistry has stabilized, you may see some etching in your plaster from the pool algae.

You may need to get a sanding block from your local pool store and sand the areas where the black algae used to be.

Chart - Super-chlorinate Your Pool
(Amount Needed to Reach 10 ppm)

Well, there you have it. I told you killing algae wasn't going to be fun, but if you have a pool with black algae, you gotta get nasty with it.

Low down, dirty, in the gutter kind of nasty. Believe me, it won't show you any mercy.

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