What Causes Green Pool Water

There are so many things that can and do cause your pool to go green. There are also many different shades of green that your water can be, all of which can mean very different things. When a customer comes in and says their pool is green, there are numerous questions we need to ask in order to decipher the exact reason why, and what we can do to make it crystal clear again.

Here are some of the reasons:

Not enough circulation and filtration

It seems silly but one of the main reasons for pool water turning green is not enough swimming! A pool needs circulation. Without circulation, everything will sink to the bottom of the pool and just sit there. Whereas if you’re swimming in the pool, scooping your pool, moving the water around, or even having a big pool party all of the water at the bottom of the pool will come up and go through the filter and help prevent algae in your pool.


When the wind blows leaves, grass, dust, etc. into your pool it can go green. Yes, it’s true; our Manitoba weather can sometimes be fully responsible for a pool turning green. Whether there’s a tree hanging over your pool, construction going on at your neighbour’s house, or the pollen in the air, all of these things can contribute to turning your pool water green.

Dirty filters

This one is huge. This is one of the first questions we ask our customers when they come to us with green pool water. If your filter is dirty and you’re trying to vacuum up the algae, you can’t expect the algae to go through the dirty filter and get cleaned. When they are dirty the algae just goes right through them and comes right back into your pool. Cleaning your filters is so important!

Improper use of chemicals

This one is pretty self-explanatory. If you’re throwing a bunch of different kinds of chemicals in there just to ‘balance’ the pool out, you could actually be causing chemical reactions such as turning your pool water green. It’s important to test your pool on a regular basis as well as follow the directions that our Water-Lab team gives when you come in for your monthly water sample visit.


This is an example of a ‘light green’ pool.


This is an example of a ‘moderate green’ pool.

Having a green pool is a pain to get rid of. We are here to help you be pro-active so you can help prevent it, or even be prepared. If you see any shade of green in your pool, bring a sample in to Aqua-Tech. Our knowledgeable Water Lab Tech’s will help you turn that water from green to blue!


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