How to Treat Moderate Swimming Pool Algae


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If your swimming pool has just started to turn green but you can still see the bottom, you need to start treating it now before it becomes a serious problem. This guide takes you through the sequence of steps you will need to follow to get your pool chemically balanced and back to sparkling clear water. Please note that while this procedure will work in most situations, it may not work in all cases. Eliminating pool algae is not an exact science and there may be other factors in cleaning your pool which have not been considered. Please give us a call at 877-372-6038 if you need more help.

Step by Step


Step 1

TURN OFF PUMP - Shut off the power to the pump. For maximum safety, turn power off at the circuit breaker to the pump.

Step 2

CLEAN OUT SKIMMER - Remove the skimmer's cover, lift out the skimmer basket and clean out the debris in the basket.

Step 3

CLEAN OUT PUMP STRAINER - Remove any debris in the pump's strainer basket.

Step 4

CLEAN FILTER - Depending on your type of filter, remove and spray off the cartridge or backwash the sand or DE filter. For more information on cleaning a filter, see our guides on How To Clean a Filter.

Step 5

TURN ON PUMP - Turn on the power to the pump. Run a VS pump at high speed.

Step 6

REMOVE LARGE DEBRIS - Using a net, remove all large debris from the surface and the pool's floor.

Step 7

BRUSH POOL -  Brush any algae off of the pool walls and floor. Brush the algae towards the main drain at the deep end.

Step 8

PUT CHLORINE TABLETS IN POOL - If you have a chlorinator, make sure it is filled with chlorine tablets. It is important to maintain a constant flow of chlorine even when using shock. Shock will spike chlorine levels for only a couple of days. If you have a Salt Chlorine Generator (SCG), leave it on. If your current algae problem is due to calcium buildup in the cell, consider getting a floating chlorinator until you can clean or replace the cell.

Step 9

SHOCK POOL - Shock your pool with a double dosage of pool shock. The instructions on most of the one-pound shock bags are to add one bag per 10,000 gallons of water in your pool. For example if you have a 20,000 gallon pool, for a double dosage you would add two bags times two which translates to four bags of shock. There are several types of shock available for your pool. We would recommend Sodium Dichlor for a fiberglass pool or one with a liner to prevent bleaching of the surface. Also use Sodium Dichlor in pools with Salt Chlorine Generators (SCG) to avoid calcium buildup on the cell plates. Use Calcium Hypo for hard surface pools with regular chlorinators. Another option is to add liquid chlorine (sodium hypo) at a rate of two gallons per 10,000 of pool water for a double dose. Liquid chlorine can be used in pools with a chlorinator or SCG.

Step 10

ADD ALGAECIDE - Add an algaecide like Sodium Bromide to help treat and prevent the return of algae. Follow instructions on the bottle.

Step 11

RUN PUMP FOR 24 HOURS - Run the pool pump for 24 hours to clear the water and to avoid mixing concentrated levels of chlorine with other chemicals.

Step 12

VACUUM FLOOR - Vacuum the dead algae off of the pool's floor
with a suction vacuum. Also check for new debris in the skimmer and pump strainer baskets.

Step 13

CLEAN FILTER - Clean your filter again. It is important to get the algae residue out of your filter.

Step 14

REPEAT SHOCK AND ALGAECIDE IF REQUIRED - If your pool still has a green tint to the water, repeat Steps 7 - 11 to purge the rest of the algae. If algae residue is light, use a single dosage for this second application. If the algae level is still high, repeat a double dosage of treatment.

Step 15

CHECK SGC CELL - If you have a SCG, you should take the cell out to see if it needs to be cleaned. One of the reasons your pool may have turned green is because the SCG cell was not producing enough chlorine. See our guides: "How To Clean a Hayward AquaRite Turbo Cell" or "How To Clean a Compupool Salt Generator Cell".

Step 16

TEST CHEMICAL LEVELS - Another reason for your algae buildup is a failure to maintain your pool's chemistry. Take a sample of your pool's water to a local pool store to have it tested. It is more accurate and is usually done for free. Be sure to tell them if you have a saltwater pool and ask them to include tests for metals and phosphates.

Step 17

ADD STABILIZER IF REQUIRED - Stabilizer (aka conditioner or cyanuric acid) is used to slow the depletion of chlorine by the sun. Stabilizer should run between 50 - 80 ppm. Add stabilizer slowly into your pool's skimmer per instructions. Stabilizer comes in two forms: solid and liquid. The liquid costs a little more, but dissolves faster.

Step 18

BOOST ALKALINITY IF REQUIRED - If your pool sample report says you need to increase your alkalinity level, correct alkalinity before correcting pH. Increasing alkalinity may also increase your pH level to a point that you will have to add additional acid to reduce pH. The ideal range for alkalinity is 80 - 120 ppm. See instructions on the side of the container for the amount to add.

Step 19

RUN PUMP FOR 24 HOURS - Run the pool pump for 24 hours. Stabilizer and alkaline can be added together, but wait 24 hours before adding other chemicals.

Step 20

ADD ACID IF REQUIRED - If your pool's pH is high, add acid in accordance with the instructions provided by the pool store or the product label. The ideal range for pH is 7.2 - 7.6 ppm. Liquid acid cannot be shipped and is generally purchased at a pool store.

Step 21

RUN PUMP 24 HOURS - Run the pool pump for 24 hours.

Step 22

ADD CALCIUM HARDNESS INCREASER - If your pool has a low hardness reading, add calcium hardness increaser in accordance with the instructions provided by the pool store or the product label. Calcium hardness should run between 200 - 400 ppm. Low calcium can cause scaling and pitting of the pool surface.

Step 23

RUN PUMP 24 HOURS - Run the pool pump for 24 hours.

Step 24

OTHER CHEMICALS - Your pool may have other issues like metals and phosphates that are not directly related to algae problems. Metals in your pool will cause surface staining and are eliminated with Metal Control. Phosphates can cause cloudy water and can be eliminated with PhosFree. These should eventually be addressed, but can be deferred to a later time.

Step 25

CHECK SALT LEVEL - If you have a SCG, you will have to check your pool's salt level. Testing can be done with test strips or by your local pool store. Depending on your brand of SCG, this level ranges normally between 2700 and 3500 ppm. Because your pool was green, your salt level was probably low and you will have to add salt. See our guide on "How to Add Salt to Your Pool". When adding salt, turn off your SCG until the salt is completely dissolved (12 - 24 hours).

Step 26

SCRUB GROUT - Lastly, over the season you may have had algae build up on the tile grout around the top of your pool. To help prevent repeat occurrences of algae bloom in your pool, you should clean the grout. For instruction on cleaning the grout lines see our guide on "How To Clean Algae on Swimming Pool Tile Grout".

Step 27

CHECK CHLORINE LEVEL - After three to four days, check your chlorine level with test strips and adjust your SCG or chlorinator accordingly. If you used a floating chlorinator, remove it.



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