Without a quality pool cover and ongoing water balance tests and treatment, the health of a swimming pool can deteriorate quite rapidly. So, if you haven't touched your pool in months, it's very likely that you'll need to give your pool a full service to ensure it's safe for swimming again.
Unfortunately, it can take several days to restore a pool back to full health, but you can typically get the job done by following these four steps:
There will likely be a layer of scum on the surface of the pool. Use a leaf net (not a skimmer) to remove debris from the water surface. Leaf nets are available at hardware stores and some pool shops.
A murky pool is likely abundant in unwanted bacteria and unsafe for use. To combat this, you need to adjust the chemicals. First, you need to determine your chemical levels by using a test strip. Then, you need to use pH reducer and increaser until you find the ideal level, which is around 7.5 and 7.8. Note, you may also need alkalinity increaser.
If there is a large build-up of algae, you need to shock the pool. Add 12-14L of shock over the course of a few days. If administered correctly, the water will change to cloudy white, light green, or clear. If nothing has changed, continue to add more shock.
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You'll need to run the pool filter 24 hours a day for a few days to clear unwanted debris and bacteria that has accumulated in the pool. Be sure to backwash your filter 3-4 times per day. Green water can clog and damage a filter, and it is normal to backwash frequently while cleaning murky pools. Note, if your pool does not clear, you should contact a pool professional to have your filtration system checked.
The final step is cleaning the pool floor. This can be done manually with a long pool brush, or with a robotic pool cleaner. However, in extreme cases of debris build-up, we recommend consulting a pool professional to ensure your pool is safe for swimming. In all cases, regularly check your pipes for clogs and filtration system for wear to avoid further damage.