Discolouration/Staining at bottom of pool

Hi guys

This is my first posting as I am a new member of SFN.

Can anyone offer some info or advise re my pool.

We’ve had a large above ground pool with vinyl lining for 8 years, and each year have been pleased that I’ve been able to get it sparkling crystal clean.

When we opened it this summer the water was particularly dark green and lots of leaves and thick algae on the bottom. The PH was very low and I had to put in loads before it was balanced. The water now is clear and balanced but there are areas of the bottom of the pool that appear to be lightly stained or discoloured. It isn’t algae as it won’t brush off.

Might it be organic staining and if so does anyone know what I can do about it?

Any help would be appreciated?



Yes chlorine is heavier than water so it will help. Eau de javel from a bricolage, unscented and in thickened will also be a cheap source of chlorine that won’t increase your CYA level.

Cheers John
I am draining the pool now and will refill later.
When the water is low, would it be okay to add some chlorine at that time, probably the dissolveable granules (predissolved of course)? A strong solution at that time might have a better effect on the staining. It won’t be circulated by the pump of course, but there will be some circulation by the incoming fresh water.

Hi Nigel,

Definitely the latter, the CYA is chemically bound to the chlorine and there is now insufficient free active chlorine to sanitise the pool or deal with organic stains.

Time to get wet!

Thanks John
We generally use the multifunction tablets to regularise and when we drained in the winter we didn’t take the level as low as we have before, so this would seem to confirm your diagnosis.
Do you think that the discolouration is linked to that,or is it because the high CYA is effecting the efficiency of the chlorine.

Hi Nigel,

Ok if your readings are correct ish and that CYA figure is around 250 you need to drain some of the water to fill with fresh so the CYA is around 50pp. Roughly 4/5ths. Dip strips are in my experience and many others hopeless for CYA measurement, yours is seriously the highest level I have ever heard anyone being able to measure with dip strips so maybe they have changed the formulation. I was at a pool just last week with 207ppm CYA and his strips were simply not showing a reading, I took a photo as it was astounding.

With you not being able to get control of your pool the test results would back up the overstabilisation with CYA so a partial drain and refill is the necessary path as trying to maintain a chlorine level of 12.5ppm to counter the chlorine bound to the CYA is getting into silly territory.

This thread at the beginning will take you through some of the chemicals you are using. http://www.survivefrance.com/group/swimming-pools



Hi John
I’m using Aquacheck strips to check levels and at present they are:
PH 7.2, Free Chlorine 3, Total Alkaliniity 180, Stabiliser 250(ish)
The attached photo hopefully shows the discolouration- the difference between the very edge of the bottom and further in.
If I chlorine shock it how high should I go? Will a big increase in Chlorine upset all the other readings? As I said in an earlier posting, this year has been particularly hard to clear the water - I suspect that when I first chlorine shocked my pH was too low.
Thanks for your help so far

Nigel, Absolutely DO NOT scrub the liner, for exactly the reason you already know. Most liners are covered with a thin lacquer coating which you could end up removing. (why does a non stick pan require scrubby sponge is a question for another day)

If as you say the staining is organic in nature raise the chlorine level and it will be removed that way. Posting your water chemical levels will help with a snapshot of where your pool water is now, otherwise it's a bit of guesswork.

I would have thought an Australian would have some tips for us! Perhaps a tinny while working :-)

I’ve been reluctant to scrub it with anything other than a cloth as I don’t want to damage the lining, particularly as we’ve had it a few years.
But i’ll give a try tomorrow when the weather is better, but gently does it!

Like your style!!!

But not too heavy on the scrubbing, liners are thin!

Try scrubbing (harder than you can with a brush) with one of those scrubby sponges for non-stick pans. It is probably stuck-on leaf-gunk. How deep is your pool? If it is shallow enough, you put the sponge under your foot & you can scrub & read a book at the same time (because otherwise it is rather dull).