Green to Clean: How to Clear Up a Green and Cloudy Swimming Pool
Do you maintain the pool yourself?
Help! The Pool is Green!
Treating a pool that has turned green? This article will get you step-by-step through how to get that nasty pool in shape. I will also cover some basic chemistry and filtering tips to prevent this from happening again.
All information is based on an in-ground home pool of average size, from 12 to 15 thousand gallons.
Six Steps to a Clean a Green Pool
- Determine whether your water chemistry is fixable or whether it's too far gone.
- Test the water to determine the PH balance.
- Shock the pool.
- Pump and filter to regain balance.
- Brush and filter.
- Maintain balance.
Each of these steps is described in detail below.
How "Green" Is Your Pool?
Because if it's too green, you may need to have it drained and acid washed. I have seen many pools that were not just green, but black. In severe cases like this, it is more cost-effective and less time-consuming to simply drain the pool and have it acid-washed. People sometimes do not like this approach because of concerns about the cost of refilling the pool. The choice also depends on the type of filtration you are using, which I will cover.
This is my general rule for determining whether the pool can be treated chemically or needs to be drained: if you can see at least six to eight inches below the surface of the water, most likely the pool can be treated chemically. An example is in the picture at the right above; you can see the top of the first stair down into the pool, depending on the water level. Once we establish that the pool doesn't need to be drained and can be treated chemically, we can go from there.
Step 1: Testing the Water
If the pool is green, obviously there is very little to no chlorine in the pool. So testing for chlorine is not very important, since you'll be shocking the pool anyway. But pH plays a very important role. If the pH is very high, the shock will turn the pool cloudy. (It will be cloudy anyway until it all filters out, but high pH will cause a VERY cloudy pool when using shock.) I prefer to use a higher-end test kit, but the cheap test strips will at least give you an idea if your pH is high or low. You want it to be low. If the pH reads high, use one gallon of muriatic acid, which should be enough. Don't worry about adding too much acid. Test the pH again after shocking and 4 hours of circulation.
Step 2: Shocking the Pool
Once your pH is 7.2 or below, you are going to start by shocking the pool with granular chlorine (calcium hypo-chloride). I suggest purchasing a 25-pound container of granular chlorine, rather than the individual one-pound bags they sell at pool stores or large chain stores. You'll save a great deal of money, and you will need the chlorine in the future for small doses from time to time. Use five pounds of granular shock, or 10 gallons (four 2.5-gallon jugs) of liquid chlorine. With the filter pump on, broadcast the chlorine evenly over the water covering the entire pool surface until all five pounds of shock or all ten gallons of liquid chlorine have been used. Be sure to use a good algaecide as well, which you can add after a few hours of circulation.
Step 3: Pumping and Filtering
What type of filter do you have? Follow these steps for your type of filter:
- Diatomaceous Earth (DE) Filter: Before anything, backwash the DE filter. Add fresh DE powder, shock pool as explained above and run the pump for 24 hours. Make sure there are no obstructions on the pool drain, such as leaves. Of course, because the pool is green, you can't see the drain, so just run a brush over the approximate place where the main drain is at the deep end of the pool.
- Sand Filter: Same as DE, except the backwash time should be a minimum of five minutes.
- Cartridge Filter: Make sure it's in good condition and rinsed thoroughly. See note in Step 4 below about cartridges.
Step 4: Brushing and Filtration
After 24 hours of chemicals and circulation, you will see an amazing transformation. Your pool should not be "green" anymore. But it will still be cloudy, and it will need a lot of brushing and filtration for the next few days. There will probably still be a few stubborn isolated green areas that need some brushing. After 24 hours of constant circulation, backwash the filter.
Special note for cartridge filters: they will need to be cleaned more often than other filters during this process: twice a day for at least two days, or until the pool is clear.
Step 5: Maintaining Your Pool
Tips for maintaining your pool:
- Use a water clarification solution.
- Make sure you have a reliable chlorinating system, whether it is an in-line, floater, or salt system. Chlorine needs to be in the pool always. Throwing a jug of liquid in it once a week isn't a good way of maintaining the pool. A simple tablet chlorine floater is very effective. You can purchase one on eBay for a reasonable price (see below).
- Clean your filter. DE filters are by far the best filter to have. Although a bit more costly to purchase at first, they will save you both time and lots of money in the long run.
Normal Filter Maintenance
- DE filters: Backwash once a month
- Sand filters: Backwash once every two weeks. (Be sure to backwash your sand filter for a minimum of four minutes. Otherwise, you will see filthy water shooting back into the pool.)
- Cartridge filters: Every three to four weeks, unless you see algae in the pool, in which case you should clean more often. Soak in tri-sodium phosphate every three months.
You may want to check out my new article, which covers frequently asked questions such as:
- Why is my pool still cloudy and green when the chemicals are right?
- I shocked the pool, but it's still green.
- How much shock should I use?
- How long should I run the pump after shocking?
And my other article answers this common question:
- How much acid should I put in the pool?
You Might Want to Look at:
- How Does Rain Affect Chemicals in Swimming Pool Water?
A look at how rainfall impacts the chemistry of pool water.
- Advanced Pool-Water Chemistry
Resolving issues with pool water when chlorine, pH, and alkalinity are in balance. Why is my pool still cloudy?
- How to Clean a Green Pool
A step-by-step guide on how to turn your pool from green to clean.
- How to Get Rid of Black Algae
- How to Lower Stabilizer in a Swimming Pool
- D.E. Filters Explained
A look at how DE filters work and how to maintain and repair them.
- How to Clean a Cartridge Filter
- How to Keep a Pool From Getting Algae
More by this Author
What is stabilizer and how to adjust it to the right level
A guide to understanding pH and the effects of unbalanced pH levels in swimming pool water.
A troubleshooting guide to clearing up your green or cloudy pool when the chemicals all seem to be balanced.