Pool Problems

Know Your Algae

Green Algae

The most common variety of pool algae. Fortunately, it’s also the easiest to deal with.

Yellow Algae

You’ll see this on surfaces – it appears as a yellow or mustard-colored dust. It’s more resistant to chlorine.

Black Algae

Attaches to surfaces, grows roots into plaster and forms a protective slime layer over itself.

Green Algae

It’s not your fault.

Chemical interactions in your pool are complex as shown below.WaterGuru SENSE along with advice in the WaterGuru app can help.

Download the WaterGuru app. Available for iOS and Android.

Most chlorine is bound to cyanuric acid (aka stabilizer) and it is the unbound active chlorine that kills/prevents algae and provides disinfection.

97% to 99% of the chlorine is bound to cyanuric acid (CYA) under typical pool conditions. Fortunately it only takes a small amount of unbound active chlorine (hypochlorus acid) to disinfect and prevent algae growth. The active chlorine level is proportional to the FC / CYA ratio. This means that you should raise your free chlorine target as the CYA level rises.

Stabilized chlorine products, such as Trichlor tabs and pucks, increase the cyanuric acid level over time thereby lowering the active chlorine level so algae can then grow faster than it is killed.

For every 10 ppm free chlorine (FC) added by trichlor, it also increases cyanuric acid (CYA) by 6 ppm. At typical 1.5 ppm FC per day chlorine usage, this represents an increase in CYA of 27 ppm per month.

Phosphates are an essential nutrient for algae growth so keeping phosphates low helps prevent algae.

Lowering phosphate levels does not kill algae; it slows down their rate of growth. With lower phosphates, one can control algae growth with a lower active chlorine level.

Kill your green algae

Step 1

Visually identify the type of algae you’re dealing with (see above).

Step 2

Refer to your most recent WaterGuru TEST results so you know your cyanuric acid (CYA aka stabilizer or conditioner) level to know how much chlorine or other products you will need to use.

Estimate the amount of CYA added to your pool since the last WaterGuru TEST. Pools using trichlor tabs may have a CYA increase of about 25 ppm per month.

High CYA (over 100 ppm)

If your CYA is over 100 ppm do a partial drain of your pool to lower the CYA level closer to 50 ppm.

Add Green to Clean and Cal-Hypo

Add 2 lbs of Green to Clean per 15,000 gallons distributed around the pool, and concentrated where the algae is most visible.

Wait 5 minutes.

Add 2 lbs Cal-Hypo per 15,000 gallons to raise the free chlorine level by 10 ppm.

Set your pump to circulate pool water for 24 hours.

After 12 hours add 2 lbs Cal-Hypo per 10,000 gallons.

After 24 hours add an additional 2 lbs Cal-Hypo per 10,000 gallons.

Medium CYA (between 50 ppm and 100 ppm)

If your CYA is between 50 ppm and 100 ppm, add Green to Clean and Cal-Hypo

Add 2 lbs of Green to Clean per 15,000 gallons distributed around the pool, and concentrated where the algae is most visible.

Wait 5 minutes.

Add 2 lbs Cal-Hypo per 15,000 gallons to raise the free chlorine level by 10 ppm.

Set your pump to circulate pool water for 24 hours.

After 12 hours add 2 lbs Cal-Hypo per 10,000 gallons.

After 24 hours add an additional 2 lbs Cal-Hypo per 10,000 gallons.

Low CYA (lower than 50 ppm)

If your CYA is lower than 50 ppm add Cal-Hypo

Add chlorine to your pool to maintain between 10 and 20 ppm FC at all times until the pool is cleared.

2 lbs Cal-Hypo per 15,000 gallons raises the free chlorine level by 10 ppm.

As an alternative to Cal-Hypo, 1.5 gallons of 10% chlorinating liquid per 15,000 gallons raises the free chlorine level by 10 ppm.

Set your pump to circulate pool water until the water is clear.

Step 3

Optionally brush any surfaces where algae have attached themselves.

Brushing the settled algae into the bulk pool water helps expose the algae to chlorine to eliminate it faster.

Step 4

Vacuum or backwash your filter to make sure you’ve removed all dead algae.

Monitor filter pressure and backwash or clean as needed.

Prevent more green algae

Step 1

If you aren’t already enjoying one, get a WaterGuru SENSE, along with WaterGuru TEST and pool chemistry advice in the WaterGuru app.

The WaterGuru system helps maintain a consistent level of disinfection and algae prevention in your pool. It does that by recommending a free chlorine level relative to cyanuric acid (aka stabilizer) level.

Step 2

Check your latest WaterGuru TEST results. If phosphate levels are above 500 ppb, use Ultima PhosFIGHT to lower the phosphate level.

Step 3

Test and adjust pH and chlorine levels as needed. Because WaterGuru SENSE is calibrated precisely for your pool, you’ll always know exactly what to add and when.

Step 4

Brush pool surfaces at least monthly, so algae doesn’t have a chance to get a foothold, particularly in areas with poor circulation.