How do i tell if i have algae or not

Algae problems in swimming pool water.
Green (cloudy) water or slimy pool walls.
Black algae. Mustard algae. Pink or white pool mold.

How do i tell if i have algae or not

Postby Guest » Mon 21 Sep, 2009 13:30

Hi all, I am from the UK and I have a 15ft diamter round above ground pool that is giving me so many problems. Basically my water keeps going dark green and I cant see the bottom, I presumed it was algae until I came on here and found out anout copper making water go green...

How can I tell if i have algae? the water looks fine if i pull a sample out (looks nice and clear) and there doesnt appear to be anyhting visible in the water and the sides are not slimy at all.....

I cant tell you what my figures are at present as I am at work and dont kow my levels of the top of my head...

One other question... I had never heard of CYA until this forum, but how do you lower it?? from what I have read people like me who use tablets in the skimmer etc to add chlorine are also increasing the CYA levels all the time and this in turn means I need more and more chlorine to do the same job... Now surly there has to be some heatlh issues for the kids if I have to start having my chlorine at 7 instead of 3 just because of the rise in CYA??

Cheers for any help so far


How do i tell if i have algae or not

Postby Guest » Mon 21 Sep, 2009 13:43

Just a quick note to add the only tablets I use in my pool are Trichloro- isocyanuric Acid tablets. We keep 5 x 20g tablets in the skimmer basket
chem geek
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How do i tell if i have algae or not

Postby chem geek » Mon 21 Sep, 2009 23:22

Unless your pH got high and/or you used an algaecide with copper in it (or your Trichlor pucks had copper in them), then it is unlikely the green is copper. Copper in the water is more like a clear green, not usually dark. I suspect you have algae that is mostly settled on the bottom. If you measure more than a 1 ppm FC chlorine loss overnight (when the sun is off the pool and you remove any pucks you've got) then you've most likely got algae.

If you've been using only Trichlor, then your CYA level may be very high. For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm unless you have dilution of the water. Even at a low 1 ppm FC per day chlorine usage, the CYA would increase by over 100 ppm in 6 months. Higher CYA levels have the chlorine be less effective unless you proportionately increase the FC level.

As for safety, the amount of active chlorine (hypochlorous acid) in water is related to the FC/CYA ratio, not to the FC level alone. Most of the chlorine measured as FC is bound to CYA and does not get absorbed through the skin nor is it volatile. If you were to drink quarts of water every day, then you could exceed the 4 ppm FC limit set by the EPA, but you don't usually drink pool water like that. However, when the CYA is so high, you don't want to raise the FC, but rather want to lower the CYA level and that can only be done via dilution of the water. To avoid the problem in the future, don't use so much stabilized chlorine and instead use chlorinating liquid or bleach.

Read the Pool School for more info, including the article on Defeating Algae and also get yourself a good test kit (either the Taylor K-2006 or the TF100 from

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