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Red Algae & Swimming Pool Chemistry

Swimming Pool Care

Learn the best way to remove red algae from your pool and what it takes to kill this algae so you can have the best swimming pool care possible.

Red algae, sometimes called red slime algae is really a bacteria. It will present itself in your pool as rust colored specks or bright reddish-pink patches on the walls, steps, and/or ladder.

It's not very nice stuff and when it come time to get rid of it you need to do all it takes. Swimming pool algae and green pool water are by far the most common complaints from pool owners.

You’ll need to chlorine shock the pool and use a swimming pool algae treatment or pool algaecide.

Red Algae Prevention

Proper balance of all your pool’s chemicals will greatly reduce the opportunity for green pool water.

Removing Red Algae

SAFETY FIRST

Always take the proper precaution in dealing with these types of pool chemicals and read the manufacture’s labels.

Use heavy duty rubber gloves and goggles and keep pool chlorine out of reach of children and pets. I recommend using granular chlorine a.k.a Calcium Hypochlorite. It’s easier, a bit safer, lighter in weight, easier to store, and 1 pound of granular chlorine equals 1 gallon (8lbs.) of liquid.

If you see that your swimming pool has red algae, you must take immediate action in killing the algae. Doing this will lessen the risk of staining and will lengthen the pool water life.

First you should:

Bring the pH, alkalinity, and hardness into line. Never add chlorine without first adjusting these three.

Adjust your pH to 7.0-7.2, alkalinity to 80-100, and hardness to 150-250ppm.

Again, I suggest you use granular chlorine, a.k.a. Calcium Hypochlorite, to shock your pool. You'll want to run your pH a little lower because pool chlorine works better at that level.

Brush the bottom, sides, and steps to loosen any swimming pool algae or red algae that may be adhering to the surface

Continuously run your filter and be sure to backwash 2 times per day until the water is clear once again.

If you have a DE filter be sure to re-coat the grids with each backwash.

Also watch that the pool’s water level does not get below a minimum of 2” from the bottom of the skimmer.

You want to get rid of the dead red algae.

Super-chlorinate, or shock, the pool bringing up the chlorine 10 times what you normally run for somewhat reddish water and up to 25 times for a more severe problem.

If your pool chlorine is 1.0ppm then raise it to 10ppm or above. You must do this in order to kill the algae.

You must reach that 10ppm or above because if you don’t it’s just wasting time and money.

To super-chlorinate you must do this all at once, not over a few hours or days. If you're running your chlorine at 1.0ppm and have solid green pool water, then bring it up to 25ppm.

Use a good pool algaecide specifically designed for killing red algae and follow the instructions on the container.

There will be dead swimming pool algae on the bottom of the pool. This can be filtered out through vacuuming the bottom of the pool.

Keep brushing and vacuuming to rid the pool and any residual red algae and remember to keep filtering and backwashing to get rid of the swimming pool algae. If you have a DE pool filter, you'll need to re-coat or recharge the grids with each backwash.

Remember when you have a red algae problem there is no quick fix. It will take time, effort, and patience to clear up your pool.

When your swimming pool chlorine is down to 1.0ppm-3.0ppm the pool will be safe to swim in once again.

NEVER allow anyone to swim in the pool until the swimming pool algae is gone and the water has cleared up.

How Much Pool Chlorine For a Good Pool Shock

Take the number of gallons in the pool and multiply by 8.34. This tells you how many pounds of water are in the pool.
Take the number 1,000,000 (a million) and divide it by the answer you have from your first calculation. This will tell you how many parts per million that 1 pound of chemicals will be present in your pool.
Take the number 10 and divide it by the answer you got after the second calculation. This tells you how many pounds of chlorine you will need to add to get 10 ppm.

Example #1

Here's an example with a 15,000-gallon pool:

15,000 X 8.34 = 125,100. There are 125,100 pounds of water in a 15,000-gallon pool.

1,000,000 divided by 125,100 = 8, well, close enough. This means each pound of chemicals added to the water will be 8 parts per million.

10 divided by 8 equals 1.25, so you'll need to add about 11/4 pounds of chlorine to get 10 ppm.

Example #2

Here's an 18,000-gallon pool:

18,000 X 8.34 = 150,120. There are 150,120 pounds of water in an 18,000-gallon pool.

1,000,000 divided by 150,120 = 6.66. Again, pretty close so we'll say 6.7. Or if you want easy math, just round it up to 7 to be on the safe side.This means that each pound of chemicals we add to the water, it will be about 6.7 parts per million.

10 divided by 6.7 = 1.49 we'll call 1.5. This means that we need to add about 11/2 pounds of chlorine to get 10 ppm.

Or, you can simply go to the swimming pool chlorine page and this will give you the chart you need to shock or super-chlorinate your swimming pool.

If you want to bring the pool chlorine level up 20-25ppm, then just double the amount of pool chlorine.

Once you're done with the red algae and the chemical levels are right it's time to swim.

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