Algae Growing Under Pool Liner

by Pat Garrett
(Kingsport, TN)

Wet/damp spots, algae under liner

Wet/damp spots, algae under liner

I need to replace my above ground liner. (21 foot round, frog system, very little chlorine). It was leaking down more and more over a few months last summer and lost half the water last winter. When I pulled up the old liner I found many spots where it looks like it was leaking. (See the photo) is that what I am seeing?

If so my 25 year liner appears to have failed across every panel.

Hi Pat

My guess, and I have seen this many times, is that the bottom of the pool was full of pin holes. Pin holes leak slowly, like you describe. The most common cause of pin holes are automatic pool cleaners. If the cleaner runs too often it is possible for it to wear holes in the liner. If that sounds like your situation just reduce the amount of time the cleaner is in use, and be sure it is always in motion, never cleaning the same spot for hours at a time.

In most cases where the algae is in the sand like that there is plastic under the sand. With no plastic the water sinks into the ground and the sand remains dry, not producing algae. There are many times when plastic is needed, so it's not a bad thing, just something to be aware of.

Before installing the new liner you should remove all the algae and probably add a little more fresh sand.

Some important things to know before going into any more detail would be how old the liner is, what brand and what thickness. Also helpful would be the type of cleaner used, if any.

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May 06, 2014
Thanks for the fast reply!
by: Pat

My wife says the pool is an Esther Williams brand. My local pool shop told me they are out of business. It is an all aluminum pool, sidewall, rails everything. I love the pool itself, it is really maintenance free. This is our fifth season with the pool.

I have an orange lady bug cleaner but did not use it last year. Instead I brush the sidewalls and floor once a week and vacuum afterwards. I have had the pool chemicals stable for about 3 years now. Basically just controlling the ph. That is until it started leaking and I was adding 4-5 inches of water a week. I love the Frog mineral system. I just drop a single chlorine tab once a week in the skimmer. I really don't have any issues algae or cloudiness.

Hi Pat

Changing from the automatic cleaner to the hand vacuum might be the problem. If a hand vacuum is allowed to bump into the wall it will cut holes in the liner. This type of liner damage usually leaves wet spots around the outside of the pool.

Back in the day when everyone used a hand vacuum it was very common for people to allow the wall to guide the vacuum around the outer edge of the pool. The results were small cuts at the top of the cove pretty much all around the pool. That's something to keep in mind when you start vacuuming again, stay 6" away from the pool wall with the brush and the vacuum head. A towel wrapped around your foot does a good job of cleaning the cove area.

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