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New pool yellow staining tide mark

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Hi, we have a new pool that’s one week old, during the early stages before using the water started to turn a green tinge. We did water test and no chlorine registered but all other quality seemed fine. Pool supplier company put in algicide and shock which cleared up water. Within days a yellow stain appeared around pool and got worse over the next few days. Nobody used any sun cream, tanning cream or any other creams that are known to react with copper based products. The algicide that was used we believe was copper based.Has anybody got any ideas to give possible causes or solutions to remove please - thank you 

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  • 2 weeks later...

I have a guess. What is your cyanuric acid level? What form of chlorine are you using? (I suspect you might be using trichlor tabs and you don't have enough Cyanuric acid buildup after a week, which is to be expected,  or a SWCG and have not added enough Cyanuric acid) also, does the stain react to chlorine and disappear (pour some bleach on it and see what happens.) If so it's algae. The fact that you had not chlorine in a week old pool  makes me suspect that t the FC is being burned off by the sun because your stabilizer is low. In addition, some algaecides (notiably polyquat) will also kill chlorine.  Yellow stains are either organic, iron, or algae. Iron would come from your fill water and if your pH was high (if the pool is plaster this is most certainly the case for teh first year!),  shocking  could cause staining . Iron stains are most common in fiberglass pools but can also appear on plaster and vinyl. . You really need to tell us more about your pool and post a full set of test results so we can better help you.


A few tests to try, hold a vitamin C tablet on the stain. If it disappears in about 30 seconds where the tablet sat then it's iron. Pour bleach or hold a trichlor tablet on a stain. If it disappears it's algae or organic.

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