Swimming pool green creases

Good morning
Probably due to the weird weather but my pool generally look’s crystal clear except for tiny green algae outbreaks on the creases.
As we have had visitors we’ve controlled it with brushing and leaving the pump on longer. We kept the chlorine around 4 to 4.5
Last Friday ( after visitors departed)I added 5 litres of javel which took my chlorine up to 14 and sustained that for easily 24 hours.
I didnt dare add any more as my sister is arriving tomorrow.
This morning my chlorine is 7.5
Free chlorine 7
Cya 62
ph 7.7
Alkalinity I haven’t checked but it’s generally around 70/80.
I still have green creases.
Should I add algaecide?

Or should I just get through the next 3 weeks and thankfully close the pool?
Also we replaced our sand filter 4 years ago so I assume it has 2 years left perhaps.
If it makes a difference we had a new pool liner at the end of March so have been running the pool for 2 extra months and the pool was fine until the weather warmed up.
I don’t really want to add another lot of javel before finally closing the pool which I have literally been in 6 times!

Those are exactly the symptoms of a neighbour’s lined pool and it was mustard algae which is highly chlorine resistant.

Your local pool shop will know which anti-algae treatment you need.

Thank you.
I’ll be honest it doesn’t look like mustard algae which I had 5 years ago but it could be.
My grandson is here until 28th so I’ll see what I can do whilst he uses the pool.

I will be interested to see what Corona says on this.

I am running my pool on pretty well the same readings as you, but do not have any green, but plenty of dark algae silt that disappears as soon as it sees a brush. The hot weather plays havoc with pools.

@Corona :wink:

Pool algaecide is an industry con trick. Chlorine is the best and cheapest and fastest acting algaecide.

Pool shops know how to sell magic potions and magic as we know is an illusion.

Now back to reality, do pool shops sell algaecide level testers? So know one knows how much they need great for sales. Chlorine burns out anything it can in the water, that means adding std algaecide will use up your chlorine quicker meaning you’ll buy more and of course the algaecide has been burned up by the chlorine so you’ll buy more of that to.
And the cycle goes on and you get a foaming mess of a pool.


That will be fine to swim in no issues as the CYA tempers down the chlorine so its actually less than an indoor pool without CYA in the water. Keep brushing and creases after a new liner? So that also means you have new water this season?
How are you testing the water figuers?

Dont let your chlorine drop below 5ppm and your shock level when you can is 24ppm (40% of your CYA level)

Would like to know your phosphate level but you would probably need an aquarium test kit for that as the pool shops of France may not carry them yet.

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OK - this is a nuisance! I hit send twice, went in to delete one of the posts and both deleted!

A precis of my post:

  1. I keep my pool to what you said all those years ago - low TA and CYA in 50 and aerate the water returns. Works a treat. No need to test often. But come July, for three months I add 5 - 7 litres of javel every three or four days. Here I should test often. But I am lazy. There are dedicated chlorine testers on the internet - put in the water and press a button - any good?

  2. If I miss a cycle of the extra javel, the olive green silt of course appears on the bottom if no one is stirring the water. Again lazy. Should brush more often! I have ten bags of the afm you recommend that I hope to install at end of week. Will this absorb and kill this what I call algae silt?

  3. Phosphate. Is this an issue only if pool is near foliage, or can all pools suffer?


  1. Yes you should test a bit more often and you will soon get an idea of how long your chlorine last and what level you are getting to.
    Cheap testers need a calibration quite often but calibration liquids are available in a few pool shops. Really didnt like the one I bought years back but they may have improved.

  2. That silt is usually pollen and dust more than algae from samples I put under my microscope.
    AFM doesnt kill it filters, the chlorine kills but I certainly hope the AFM can capture the fine silt. The best filtration is also using the correct flow rate 20m3/m2 of filter so a 620mm filter has around 0.3m2 filter surface, so a filtration rate of 6 m3/ hour. That as said before saves a huge amount of electricty so paus for all the other parts you spend on. If you are not vacuuming the bottom then brushing to stir it up will work but could take longer.

  3. All pools can suffer as phosphates can drift in on the wind especially in rural agricultural land. Bird poop is off the charts phosphate wise, that why you see so much algae and lichen on roofs.
    Mine has gone up over the winter drastically so I used phosphate lowering NoPhos.

Thank you.
I think i knew i was tinkering and not shocking the pool properly.
I wont bother with algaecide.
I’m using a Scuba 2 for the first time. I also use a Fas dpd Taylor chlorine test for accurate chlorine levels.
I’m not hugely impressed with the scuba.
The liner isn’t creased its the natural shape of the pool as it gets deeper, its very well fitted. I didnt know how to describe it.
I may have to go to the pool shop for a phosphate test.
How long would a shock of 24ppm take to return to safe levels obviously depending on sun?

Also we have friends who had a leak , probably due to last years hot summer, the expert thinks their pipes for the jets are broken.
The solution was to bypass them and put a waterfall at the opposite end.
So four jets no longer in use and the pool is like a swamp. It’s clear for a ?4ft diameter where the waterfall falls.
It just looks stagnant at the derp end.
They have now shut off two skimmers and using the pull of the pump on the skimmer at the deep end.
They dont have weir gates either.
90m3 i think the pool is.
What would you have suggested @Corona.

That very much depends on how things go. From memory with 60ppm of CYA you can go to 12ppm of chlorine which would still be less than 5ppm of free chlorine in an indoor pool so thats about the max. I will look it up on my tables later but being an outdoor pool any nasty combined chloramines will be wafted away on tje breeze so that should give you some time to increase the chlorine and have it drop back. The only pool shops that might have a phoshate test is those using the La Motte spin touch tester, the others will just look at you blankly.

Did they actually pressure test the lines, if not they are not experts.

Weir gates prevent dirt flowing back when the pump shuts off and to a lesser degree surging due to swimmers and jumping in.

Doing a proper test and repair, deep ends need water flow as has become pretty apparent. If they use a pool robot for clraning they at least get things moving and mix the water and chemicals around. Thats how I cured the issue on a Desjoyeux pool when I first came to France, the water only flowed half way up the pool so everything at the top end was a swamp.

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Yes, he had à pressure test. I think the waterfall was considered an adequate repair but hasn’t worked in practice.

Not a surprise, pool builders just do not inderstand fluidics which is why very little advancement gets made in the pool industry.
See if you can find out where the actual fault is in the pipework, they should have been able to locate it, normally a join.

A pool robot might help stir up the water.

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Can’t tell you what to do with your pool, but HOW do I prevent a mass of wasps and bees on it in the sunlight? I have put out alternative water

Whilst I dont have a problem with them and the tiny sips of water they need, there are things in pool shops that are meant to dissuade them from the water. I have never looked into what they actually are chemically and whether it would be bad from a filtration/water chemistry point of view.

When I had a pool, one year I bought some (quite expensive) galettes containing some form of citronella designed to deter insects. They didn’t work :roll_eyes:

It’s tricky because they’re drinking rather than feeding.
Last year we had bees on the tarpaulin, when we came to open the pool I recreated the conditions so took some of the murky pool water and a dash of grenadine plus honey and a pinch of salt, mixed it up leaving it near the pool and gradually moving further away.
This worked really well.
I think perhaps if you’re getting a lot of wasps you need to look for a nest nearby.

I once tried to explain why the returns need to induce a rolling vortex in the water and the chap I was talking to looked at me like I’d started speaking Martian.

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