If algae are already visible on the pool wall, or if the pool walls feel slimy to the touch, then you have an algae infestation. If your pool water is green because you filled it with well water and chlorinated it shortly thereafter, there is almost certainly a metal failure.
Metals: High levels of metals such as copper or iron in pool water can lead to green water. This can happen if you use well water to fill your pool or if the pool's metal components, such as its ladder or pump, begin to corrode.
If you decide to fill right from the well, you can use hose filters and treat with sequester chemicals while filling to minimize staining. Let the pool run a few days before adding chlorine, and add chlorine slowly. Clean your filter frequently.
A pool turns green when there is algae in the water. There are several reasons why algae could grow, but it is most commonly caused by prolonged exposure to the sun, rain and temperature spikes. These factors affect the chemical balance of the pool and result in the pool turning cloudy and/or green.
Typically, algae is the source of green pool water, and it's certainly possible that it took over quickly, even overnight. This is especially likely if it is very warm outside, since algae blooms more rapidly in warmer temperatures.
Shock the pool weekly. Shocking helps reduce cloudy water, which could be an indicator of early stage algae growth. Pools are generally shocked with concentrated forms of chlorine like calcium hypochlorite or dichloride. Calcium hypochlorite is a granular chlorine oxidizer that adds chlorine and calcium to water.
Very few wells will need more than one gallon of bleach. Using more bleach than necessary will not disinfect the water faster, may cause corrosion of the steel casing and will hinder the disinfection effectiveness. To calculate the amount of bleach needed, you need to know the well's depth and static water level.
Non-Algae Cause: Copper Ions
Another reason your pool could be green is if your water has high levels of copper. The chemical balance of your pool can easily be thrown off, causing problems across the board. Regular testing and balancing can help avoid these problems.
Well water contains many metals like rust, iron, copper, manganese, and cobalt. These metals cause pool stains and water discoloration.
If using bleach, pour 24 ounces per 100 gallons of water into the well through the vent hole (see table below). If using granular chlorine/calcium hypochlorite, pour 3 ounces per 100 gallons of water into the well through the vent hole. 6-inch diameter wells have 1.5 gallons of water per 1 foot of well.
Test and treat the water during filling and before swimming. Depending on the water quality and your preferences, you may need to treat it with some combination of chlorine shock, chlorine or bromine, algaecide, a sequestering agent for hard water and metals, pH corrector, and pool clarifier.
Clear pool water with a green tint may be from pollen, chlorine-resistant algae, or most often from a too-high pH level. When a pool's pH is over 7.8, even high levels of chlorine destabilize and cannot sanitize, and metal in your water and pool components can oxidize, giving off a greenish hue.
Baking Soda and Green, Blue, or Yellow Algae
You'll need to use an algaecide to kill the algae and superchlorinate your pool to clear the water. After this treatment, test your pH and alkalinity and add baking soda to raise alkalinity to at least 100 ppm and pH to between 7.2 and 7.8.
Liquid chlorine in the form of household bleach and food grade white vinegar can be used to disinfect your well. When chlorine is added to water the pH level will rise. Food grade white vinegar is used to lower the water's pH level so the chlorine will work effectively.
Depending on the size and depth of the well and extent of contamination, pumping times will vary; it may take thirty minutes, or it could take several hours or days until the water runs clear.
Chlorination is effective for getting rid of a one-time case of bacterial contamination.
There's a protocol when using Clorox® Disinfecting Bleach for swimming pool disinfection to prevent algae growth when a pool is in use: on an ongoing basis, if you super-chlorinate the pool with 6-12 cups bleach per 5,000 gallons of water, in addition to regular chlorination, algae growth can be prevented.
Use a quadruple dose of shock. One pound of shock treats 10,000 gallons of water. So if you have a 20,000-gallon pool, and your water is dark green, you'll need 6 bags of shock. That's a triple dose.
Pools can immediately turn green after being shocked when they have metals like copper in the water. These metals oxidise when exposed to high levels of chlorine, which makes the pool water turn green. Adding a metal control product such as Zodiac Metal Remover will help to restore the pool water.
What should I do if my pool is dark green and I can't see the bottom? If your pool is dark green and you can't see the bottom, you may need to add a clarifier or flocculant the next day to remove the dead algae.
Green algae welcome the growth of bacteria like E. Coli. By choosing to swim in a pool with algae, you run the risk of developing a rash, infection, or illness. We highly recommend contacting a professional and taking care of your green water woes before entering your pool.