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My above-ground pool got infested with algae. I tried shocking it but that didn't work. I covered, the pool and went off on holiday for a week leaving the pool with no pump running - and no-one using it.

When I returned from holiday, the algae was still bright green and alive (as expected) - but had all dropped out of suspension and was now on the bottom of the pool (unexpected). The water was crystal clear.

I started vacuuming the bottom of the pool and, sure enough, the algae was lifting out nicely, revealing the clean pool bottom.

After some deliberation, I decided to empty the pool and re-fill it, but I'm wondering, would it have been a viable solution to vacuum all of the algae and give the pool another shock, for good measure? If so, it seems like a nice, simple solution to curing algae rather than all the testing, shocking and chemical balancing that I was trying initially....?

  • Water is water. Filters filter particles out of the water. Yes you could have saved your water. With algae bloom like that it sounds like you have high phosphate levels tho. No phosphates and algae has no source to grow from. As far as algae being easy to clean up, it’s generally not because it clings to things. Live growing algae is a natural water filter tho, which was responsible for your crystal clear water. – Tyson Aug 23 '18 at 10:32
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After some deliberation, I decided to empty the pool and re-fill it, but I'm wondering, would it have been a viable solution to vacuum all of the algae and give the pool another shock, for good measure?

You didn't need to empty your pool. Plenty of people run into Algae attacks, it's not exactly the end of the world.

When you say you shocked your pool, you need to be way more specific on what you mean by that. There are guidelines out there that go into detail about how to shock a pool.

If so, it seems like a nice, simple solution to curing algae rather than all the testing, shocking and chemical balancing that I was trying initially....?

First off, shocking the pool can be done in 2 ways.

  1. Using a powder shock mixture that may include Calcium or Cyanuric Acid including a High percentage of Hypochlorite (chlorine).

  2. Bleach/Chlorine is the second method.

The reason why pool owners are required to maintain a specific level of chlorine is to fend off algae attacks. The fact that you turned off your pool pump had nothing to do with why you got attacked, but because your chlorine levels are probably 0 ppm (parts per million).

Now, I would agree with you that shocking a pool, and constantly testing is costly and annoying. But depending on where you live, emptying your pool can be even more costly. If your pool is 30,000+ gallons. Get ready for your water bill to triple that month. Shocking your pool might only cost a fraction of that price.

I was just trying to ascertain whether vacuuming the algae from the bottom/sides would have left the water as clean as it appeared to be...?

No, Even with your filter at 100% Clean and functioning. Algae is cleaned with a killing agent (Chlorine). Not your filter. The filter is mainly used for collecting dirt (AKA DEAD ALGAE).

Lets say you swept the sides of the pool and vacuumed the remaining algae.

First, the odds of you cleaning every inch of your pool is unrealistic. There are going to be nooks and crannies where algae will remain and then begin to grow all over again.

Second, lets say 99.9% of all the green algae got stuck in your filter. Your filter isn't going to kill the algae, it's just going to sit in your filter. And eventually break away from your filter and move back into the pool. You have to kill the algae. The dead algae then gets collected back into your filter and stays dead.

Don't you think if filters could simply catch all algae and kill it, the chlorine industry would have dead off long ago? People would install 2 or 3 filters and avoid ever paying and arm and a leg for chlorine on a yearly basis.

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  • A great answer - but not really an answer to this question. I'll admit that I didn't use either of the chemicals that you mention - just a huge dose of my normal Chlorine granules - but, with the pool covered and the pump OFF, the algae all settled to the bottom, leaving the water clear. I was just trying to ascertain whether vacuuming the algae from the bottom/sides would have left the water as clean as it appeared to be...? – Lefty May 17 '19 at 13:56
  • It depends on the condition and capacity of your filter. I've dealt with this in the past and used a specific anti-algae product that included copper. Killed the algae dead, vacuumed it up, and refreshed the filter. Before vacuuming, brush down all the walls/steps to get everything on the bottom. – Tim Nevins May 17 '19 at 15:19
  • @lefty I edited my post to further explain my answer. – Sickest May 17 '19 at 17:45
  • I understand why you read my question the way you do - but perhaps I should have made it clearer. There was no suggestion whatsoever that I NEVER use Chlorine again - far from it. I was basically asking if vacuuming the algae would remove enough of it to treat the residual fairly easily with chemicals. It certainly seemed like it might, because the water appeared to be very clean. It is only a 3m fast-set pool so refilling was not a massive problem and I didn't take the risk. – Lefty May 17 '19 at 17:52
  • I never asserted you never used chlorine ever again. Cleaning up algae does NOT make the treatment easier. I answered your question Lefty, Filters do not kill algae or remove algae that's alive. The water appeared to be clear, because it was all in your filter. Which would have then gone back into your pool. You would have still needed to use the same amount of chlorine to shock your pool. If you don't want to accept that. So be it. Good luck with you. – Sickest May 17 '19 at 17:57

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