Green water algae or floating algae are a common problem in swimming pools. The treatment involves a variety of chemicals and waits a few days if the algae builds up. You can prevent algae from coming back into your pool through regular pool maintenance.
Step
Method 1 of 3: Getting Rid of Green Algae with Chlorine
Step 1. Use chlorine to kill algae
When the pool water is green or clumps of algae are clearly visible in the pool, it means that the pool water does not contain enough chlorine. Pouring large doses of chlorine into swimming pool water is the most effective way to kill algae and restore pool cleanliness. This method usually lasts for 1-3 days, or maybe more if the pool conditions are severe enough.
The other methods listed below take less time, but may not restore the cleanliness of the pool. These methods are also more expensive and have side effects
Step 2. Brush the pool walls and floor
Brush vigorously to remove as much algae as possible. This will reduce the time needed to eradicate and stop algae growth. Pay particular attention to steps, behind climbing ladders and all corners where algae usually gather.
Make sure the brush used is suitable for the pool. Iron brushes are great for concrete walls, while nylon brushes are recommended for vinyl pools
Step 3. Review the safety of the chemicals for the pool
You will be using hazardous chemicals during this method. Always read the safety information on the label first. At a minimum, follow the following safety standards that apply to all swimming pools:
- Wear gloves, eye protection, and clothing that protects the skin. After use, wash your hands and inspect clothing for traces of chemicals.
- Do not inhale the chemical. Be careful when using chemicals in windy weather.
- Chemicals MUST always be added to water, not water added to chemicals. Do not put the wet dipper back in its container.
- Store chemicals in closed, fireproof containers, out of reach of children, and on separate shelves on the same level (don't put them on top of others). Many chemicals explode if they touch other swimming pool chemicals.
Step 4. Adjust the pH level of the pool
Use a swimming pool pH meter to determine the pH level of your pool. If the pH is above 7.6 (common during algae growth) add a pH reducer (eg sodium bisulfate) according to the instructions on the package label. A good pH level is between 7.2 to 7.6 to make chlorine work more effectively and reduce algae growth. Wait a few hours, then test the pool pH again.
- A measuring device in the form of a tablet or a dropper is much more accurate than a measuring paper strip.
- If the pH level returns to normal but total alkalinity is above 120 mg/L, check the pH lowering label for instructions for restoring total alkalinity to between 80 and 120 mg/L.
Step 5. Select the appropriate shock chlorine product
Chlorine used for regular pool maintenance is not a good choice for algae cleaning. Ideally, use a liquid chlorine product specifically designed for swimming pools. This product contains sodium hypochlorite, calcium hypochlorite, or lithium hypochlorite.
- Avoid calcium hypochlorite if you have hard water.
- All hypochlorite products are flammable and explosive. Lithium is quite safe, but more expensive.
- Avoid tablet or granular chlorine products (eg dichlor or trichlor), which contain stabilizers that should not be put into swimming pools in large quantities.
Step 6. Administer a slightly excess dose of chlorine
Check the product label for the “shock” instructions. To get rid of algae, use twice the recommended “shock” amount. Make it three times if the water looks very dark. In fact, quadruple it if the top rung of the ladder isn't visible at all. After the pool filter is turned on, apply chlorine directly to the pool perimeter. (If you have a vinyl pool boat, pour the chlorine into a bucket of pool water to avoid bleaching).
- Attention: liquid chlorine will explode and produce a corrosive gas and if it comes in contact with chlorine tablets or granules. Never pour liquid chlorine into a pool skimmer or anything containing this product.
- Since UV in sunlight decomposes chlorine, it is best to wash it at night and leave it overnight.
Step 7. Check the pool again the next day
After the pool filter has worked for 12-24 hours, check your pool. Dead algae turn white or gray, and they float in the water or sink to the bottom of the pond. Do a test measurement again to see the new chlorine level and pool pH.
- If the chlorine level is higher than initial (2–5 mg/L) but algae is still present, simply maintain this chlorine level for the next few days.
- If the chlorine level has risen but is still below 2 mg/L, perform another shock the next night.
- If there is no significant difference in chlorine levels, your pool most likely has too much cyanuric acid (more than 50 mg/L). This is due to the use of tablet and granular chlorine and “locking” your chlorine into an unusable form. The only way to fight it is to do repeated shocks, or drain some of the pool water.
- A lot of dry leaf litter or other objects in the pool can also deplete your chlorine. If the pool hasn't been used for a long time, you can spend a whole week doing a few shocks.
Step 8. Brush and test daily
Brush vigorously to fight new algae growth on the walls. In the next few days, the chlorine should have killed the algae. Do the test daily to make sure the chlorine and pH levels are correct.
A well maintained swimming pool has the following levels: Free Chlorine: 2-4 mg/L, pH: 7.2 – 7.6, Alkalinity: 80 – 120 mg/L and Calcium Hardness: 200 – 400 mg/L. It's okay if the numbers have a slight difference, a slight deviation shouldn't be a problem
Step 9. Suck up dead algae
When there is no more green in your pond, suck out the dead algae until the water is clear. You can skip this step and let the pool filter do the work, but only if you have a strong pool filter and are willing to wait a few days.
If you're having trouble getting rid of all the algae, add a coagulant or flocculant so the algae clumps together. Both of these materials are available in stores, but may not be worth buying if the pool is a home pool
Step 10. Clean the filter
If you have a D. E. filter, set the setting to low tide. If you have a cartridge filter, remove and clean the cartridge with a high pressure hose, followed by liquid muriatic acid or liquid chlorine if needed. If the filter is not cleaned thoroughly, dead algae can clog the filter.
Method 2 of 3: Other Ways to Get Rid of Green Algae
Step 1. Increase circulation to tackle tiny spots of algae
If the algae form small clumps but don't spread throughout the pond, you likely have an area of stagnant water. Check that the water jet is working properly. These jets must point to the water at a certain angle, so that the water flows in a spiral pattern.
Step 2. Collect algae with a flocculant
The flocculant or coagulant collects the algae together, so that the algae collection can be sucked out. This method is quite tiring, but the pool will be clean in a day. This is the quickest way to keep your pool looking clean, but pool water isn't necessarily "safe" for swimming. Like algae, viruses and bacteria can reproduce. It is best to combine this method with a chlorine shock to clean the pool, and do not swim until the chlorine and pH levels have returned to normal.
Step 3. Clean the pond with algaside
Algasides (algal toxins) are guaranteed to kill algae in ponds, but the side effects and costs may not be worth using. Here are some factors to consider this option:
- Some algasic products, however, are not strong enough to kill live algae, especially if there is also black algae in the pond. Check with pool store employees to find the right product, or look for products that have 30%+ active ingredients.
- Quaternary ammonia algasides (“poly quats”) are fairly inexpensive, but cause water to bubble and are a nuisance to many people.
- Copper-based algasides are more effective, but expensive. These algasides also usually leave stains in the pond.
- After adding the algaside, wait at least 24 hours before adding other chemicals.
Method 3 of 3: Preventing Algae Coming
Step 1. Treat the pool water
Algae will not grow if you maintain the chemical level of the pond water surface. Test regularly to see the pool's chlorine, pH, alkalinity, and cyanuric acid levels. The sooner the problem is detected, the easier the recovery process will be.
Ideally, do the test daily, especially in the first one to two weeks of algae growth. Always do the test at least twice a week during swimming season
Step 2. Give algaside as a preventive measure
Algasides are best used in small doses on a weekly basis when pond conditions are normal. Algasides will kill algae before they can grow. Check the product label for instructions for use.
Be sure to follow the instructions for regular prevention, not when algae is growing. Too much algaside can cause pools to stain and foam
Step 3. Remove the phosphate in the pond
Algae feed on various nutrients in the water, especially phosphate. Use a cheap phosphate test kit to see the phosphate content in pool water. If there is enough, use a strong commercial phosphate remover. This washer can be purchased at a swimming pool shop. Let the filters and vacuum cleaners remove the phosphate for a day or two the next day. Shock the pond when the phosphate level is at a reasonable level.
Professional swimming pool experts have differing opinions regarding reasonable phosphate levels. 300 mg/L should be low enough unless the algae problem persists
Tips
- Heat and sunlight decompose chlorine and accelerate algae growth. Keep a close eye on chlorine levels during hot, sunny weather.
- Keep an eye on the pool filter system during the shocking process. Set it to low tide completely or clean the filter whenever the pressure rises 0.7 atm (10 psi) above normal operating pressure. The dead algae that the filter collects will get dirty quickly and should be cleaned frequently.
- During winter, buy a mesh pool cover that prevents debris from entering the pool, but still allows water to pass through.
- If you have time, give half the recommended amount of pool chemistry, then add the rest if needed a few hours later. This will reduce the risk of applying excessive chemicals to the pond (if this occurs, adjustments will be more difficult.)
