Why do swimming pools turn green? What makes a swimming go green in colour

If you are a swimming pool owner, and have had your pool for a long time, you might be familiar with green swimming pool syndrome, and how to fix it.

 But if not, and you are new to owning pools and all of the joys of pool maintenance this post, drawn from personal experience may be of help.

 When it comes to private swimming pools, perhaps a backyard pool, above ground, in ground or otherwise, there are two main sorts. These are chlorine pools and salt water chlorinated pools.

 The aim of both systems is the same, to keep the water clean and safe to swim in. By safe, we mean keeping bacteria and algae at a non hazardous level.

 The owner of a chlorine pool does this by putting a measured amount of chlorine in the pol and checking it. How much goes in depends on the size of the pool and the weather Hot weather and sun will cause the chlorine to break down quicker. Evaporation and rain will also affect the chlorine balance of a pool. A salt water chlorinated pool still uses chlorine, but it does so by converting normal salt to chlorine.

 When not enough chlorine is present in the pool, algae and bacteria will begin to multiply. They do this causing the water to go hazy. This is a warning sign. If your pool starts to appear hazy, you be to either add chlorine or run your salt converter. At this stage your pool is not clean enough to swim in safely.

Swimming in a green pool runs the risk of ski irritation ad bacterial infections. If there is not enough free salt in the pool, the electrolytic converter will not have enough salt to convert to chlorine, so you will need to add salt first.

 If you don't do this, the growth of algae and bacteria increases exponentially, and large clumps of algae will start to form. It is this green algae that gives the pool the green look. By now, if you have a salt water pool it is now too far gone to recover using just the pools chlorinator. When a pool is clear and safe the salt water chlorine converter will make enough chlorine to keep things healthy but once the algae growth has rocketed most chlorinators will not make enough to reverse the situation.

You will need to shock treat your pool with a high dose of chlorine and algicide. I have covered that in another post here.

Fixing a green swimming pool - step two - balancing the PH, hardness and alkalinity levels

Before we get stuck into the detail of this post about all things pool chemical, we need to set the scene.

We inherited a green pool. We needed to clean the pool and fix it. 35000 litres in capacity. Here's how. Before we can balance it we needed to shock it with chlorine and algae killer. This done, we let it settle for a few days before stirring again and running the filter.

After about ten or 12 days the pool was starting to look a bit more swimmable, however there was more work to be done before we could get swimming.

I needed to add salt - as it was a salt chlorinated pool, and I needed to be sure that the hardness level was right, as well as the Ph level. Too much acidity or alkalinity will affect pipes and liners, as well as the electrolytic converter that changes the sodium chloride - salt - into chlorine.

Now I did year 11 and 12 chemistry but this called for a specialist. So out came the trusty sample bottle - once the coca cola was sorted - and off we went back to Clark Rubber.

Now I do need to say that this is not an ad for this business, but they were very helpful. Most pool specialists would provide similar services I imagine. They told us that the water was too soft, and that we needed to raise the alkalinity - it was too acidic. And yes that means they sold us the necessary chemicals. Fair enough I say.

So we also bought three 20 kilo bags of pool salt and stirred the whole lot in to our 35000 litre inground solar heated swimming pool. Then ran the filters....and waited....and waited.....and.....

The salt level was perfect....

The PH is now perfect, as is the water hardness level....

All we needed to do was let the chlorinator do its job and run the filter a bit more. As the chlorine level came up our once murky swampy pool began to look very good indeed.

And the end result......

Salt water chlorinated in ground swimming pool

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