Three Types of Pool Algae

As an owner of a residential swimming pool dealing with algae especially when the water is warm is not uncommon. As summer drags on and the warm water remains in a swimming pool there are a variety of reasons why algae might grow in your swimming pool. But please note, you can and will develop algae in your swimming pool during the winter time if you don’t properly take care of it. Some of the most common reasons why are the following:

  • Not enough chlorine or whatever sanitation you use
  • Lack of enough salt or too much salt if you own a salt chlorinator
  • High levels of phosphates
  • Unbalanced water chemistry
  • Not filtering your pool water long enough
  • High Cyanuric Acid (CYA) levels
  • Not keeping your pool, skimmer, and pump baskets free of debris

Types of Algae in Swimming Pools

Before you can start tackling and removing the algae it is going to be extremely important to determine what type of algae you are dealing with. In swimming pool water, you will either find green, black, or mustard algae. Green is by far the most common and black is the most challenging to remove.

  • Green Algae – This is the most common algae found in pool water, green algae will typically show up on the walls of your pool or along the surface of the water in large, floating clumps. Typically this form of algae has the largest surface area. If properly treated it can also be the easiest to remove.
  • Black Algae – This is the most difficult type of algae to remove. Black algae like to form on the interior finish of your pool and deeply root itself in the cracks and crevices. If you have a Pebble Tec swimming pool, black algae love those even more. It’s gonna take a lot more than high chlorine levels and brushing to remove.
  • Mustard Algae – mustard algae is a form of green algae that is highly resistant to chlorine and has a brownish-yellow color. This type of algae is slick and slimy, which can help you distinguish it from dirt, which will have more of a coarse feeling. This form of algae collects on pool stairs, ladders, and near pool lights.

How To Remove Algae

If you have identified that any one of the above forms of algae is in your swimming pool you will need to make sure you first balance your water chemistry. This means making sure your pH is between 7.2 and 7.6, that you raise your chlorine levels far above the normal levels, and you keep it as clean as you possibly can. If you don’t already have one you will need to purchase a steel algae brush to help break up the algae. Remember, black algae are extremely difficult, so you will need to typically brush 3-4 times a day or more. We recommend tripling up on your normal amount of shock levels and run your pump longer to help filter the swimming pool. In the end, when you finish brushing chances are you will need to brush more. In some cases, you will need to also check your phosphate levels because if they are high no matter how much chlorine you have in the pool algae will grow. One other thought is the high Cyanuric Acid levels. The normal range for a chlorine pool is between 30 – 50 ppm. CYA is like sunblock for your swimming pool preventing chlorine loss but when levels climb it can “bind” up your chlorine and render it ineffective. The multiplier to figure out how much chlorine (in ppm) you need is .075.   In the case of a pool with 60 ppm CYA, we would take 60 times .075 to get a minimum chlorine residual (or free chlorine) of 4.5 ppm.  That is why when CYA climbs above 100 or more you might need a minimum of 7.5 ppm free chlorine to prevent algae from forming. When this happens, we recommend a water change.

If you should have any questions about algae and how to remove it, we highly recommend contacting us before someone sells you on products you probably don’t need!

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