I have found that the best & fastest way to clean up a problem like that is to vacuum straight out to waste. Re-fill and do it as many times as it takes until you have just a mild green. Then shock & run the filter. This process is time consuming since you have only a short time to vacuum before the water level dips below skim line. when re-filling get the water level as high as possible by closing the valve or moving it to filter. As to why it happened....I don't know, but hope this answer will help on getting it cleaned up.
ANSWER::
It happened because maintenance was not performed on the pool -- chlorine levels maintained, shocking the pool about once per week, adjusting the pH and alkalinity. Neglect is a word for this. If you do not have a vinyl liner do the following:
Back wash filter
add 4 gallons of 12% chlorine
add either one bottle Yellow Treat or Yellow Out, as per instructions on label.
Filter for 24/7 unless Yellow Treat indicates otherwise. One bottle should be sufficient.
Brush walls and floor thoroughly using a pattern so that you do not miss a square inch of plaster in the brushing --- 2 - 3 times daily until ALL signs of algae are gone.
Back wash filter again next day.
By 3rd day things should be looking brighter.
Maintain then on 1.5 to 3.0 chlor.
72-.2 - 7.6 pH
Readjust your chlorine to 3.0 - 5.0 again
Green
swampy leaves and water and dirt
You have to treat pool water with pool chemicals and use a pool filter to get and keep the water clear.
The color of the pool is no problem at all. If the water is green, who in his right mind would jump in?
It is not the salt water pool or the salt water that is turning your hair green. It is a poorly maintained pool with a chemical imbalance - pH and total alkalinity out of required parameters.
I am not sure why this has not been answered. The most common reason for the green is algae growth. If you put on a solar cover and ignore pool maintenance, then the algae will grow as the water heats and when you remove the cover, the pool will be green
You must first determine the cause of the green water - then rectify that. The green water could be the result of the equipment not functioning correctly, or not being operated correctly, or being undersized for your pool. Or it could be a water balance problem.
Your pool water may have turned green even after adding Fresh and Clear because of metals in your water. It is likely copper that is causing the water green. Your pool store will have products available to remove the metals and clear your water up. You might also have algae if you are not putting enough chlorine in the pool.
Green pool water is caused by algae. To remove the algae, bring the pH level of the water to 7.8, scrub the sides and bottom of the pool, shock the water with chlorine, then vacuum up all the dead algae.
Shock it. Sold at Walmart, Lowes, or possibly your grocery store.
The pool water is green because of algae- which is a type of plant. You just need to add more chlorine to kill off the algae...
To me Alligators are greenish- blue or swampy green