A fair number of the pools every year that we convert to Aquafirst are green when we arrive. The owners have given up on the unending task of manually keeping the water clear. Combined with a scientific understanding of what makes your pool go green and a bit of practice we’ve perfected our method for fixing green pools, starting with why.  

Why is my pool green?

What you see when your pool is green is the presence of algae. Algae spores enter the pool a number of ways, for example, due to wind, dirt, pool equipment or bathers. Avoiding algae spores is almost impossible, however, your sanitiser usually kills them off before they become a problem. Algae spores, high phosphates (algae food) and low sanitiser can cause a pool to go green overnight. Depending on how quickly you catch it, it can be a quick fix or can take up to three days to fix.  

Why is having a green pool bad?

An untreated pool has the potential to carry bacteria and viruses which can cause a range of health problems such as ear infections and skin irritations. Green pools also pose a safety risk if bystanders cannot see a swimmer struggling at the bottom of the pool. If left untreated for long enough, pools can also become a nesting ground for mosquitoes. The best option is to prevent your pool from going green if you’re thinking ‘uh oh, too late’ check out the steps below to get your pool back to its pristine state.  

How do I fix my green pool?

Here’s our step by step guide. With good measurements and the right chemical volumes we can reliably “dose” a pool and walk away with confidence that it will come good. The only intervention is a bit of back washing to clear the flocculant from the filter, read on. 1. Set the pump running We’ll need to circulate the water continuously for the next 24 hours or so. Both to mix the chemicals we’ll be adding and remove the dead algae. 2. Add chlorine We give the pool a big dose of chlorine (super-chlorination is the industry term). This kills the algae that are making the pool green. 3. Correct the pH The wrong pH rapidly reduces the effectiveness of chlorine. Take a measurement and add acid to lower the pH or alkali to increase the pH to bring it within the optimum range. 4. Check cyanuric acid Commonly known as a stabiliser, unlike chlorine, it is persistent in pool water. It’s only diluted by water changes (draining and topping up). Too much cyanuric acid locks up too much of the chlorine stopping it from killing the algae. We check the level and reduce through water changes if it’s too high. 5. Clarifier / flocculant With a good dose of chlorine and corrected pH the algae will be killed, being bleached in the process. This leaves less green but cloudier water from all the dead bleached algae. To remove them we use a flocculant that makes them clump together so that the filter can remove them from the water. 6. Backwash The dead algae now trapped in the filter needs to be removed to keep it working efficiently. You need to periodically backwash the filter (say 2-3 times per 24 hours depending on how much algae there is) to send it to waste. 7. Slow release flocculant A really green pool contains a large amount of algae. We need to get rid of all of it. To help with the task add a slow release flocculant tablet to the skimmer box. 8. Phosphate level test Lastly we test the phosphate levels in the water. Phosphate is a fertiliser that will promote the growth of algae. It can enter the water from garden run off and bird droppings. If the levels are too high it could be contributing to the algae problem. To treat was use a phosphate remover (commonly called starver). That’s it. Sound complicated? It is, and keep in mind this a general guide only. If a pool is going green on a recurring basis there’s likely to be a root cause that warrants investigation. Let’s face it, even once you know how to fix your green swimming pool there are better things to do with your weekend and things to spend money on than pool chemicals. Sign up for the Aquafirst system and a) your pool won’t go green in the first place, b) in the extremely improbable event that it did (never say never), our monitoring would alert us and we’d send someone to fix it – free of charge.  

How do I prevent my pool going green?

It can be simple to prevent your pool from going green overnight. Just follow this simple tips and your pool will stay clear all year round:
  • Keep your sanitiser levels up
  • Run your filter for around 8 hours a day in summer and adjust accordingly for the colder months. Backwash or clean cartridges often
  • Regularly clean baskets and vacuum to remove organic matter
  • Test water chemistry whenever you clean baskets
  • In May and August, add a copper based algaecide