White substance on the top of our pool

EvelynMF

Member
May 22, 2023
10
Portugal
Chlorine
Liquid Chlorine
Hi there. We have a very large pool that we recently gave an acid wash (muratic) to remove scale build up from bore water. The pool had no issues before this. Water very clear and nothing floating on top. We do however have a leak in our skimmer boxes, so we have been avoiding using them, but this was also the case before the acid wash, so no change there.
Since refilling the pool, about a month ago, we have found white floating subtance that firstly resembles talcom powder, but then clumps together to look a bit like torn up tissue. After time it becomes harder and the particles larger, so that if you dip your arm in it, it leaves white particles the size of tiny ants on your arm. The powder reacts to acid - it fizzes. When you pick up a clump and roll it between your fingers, it forms a thread like substance. (Will include photos) The particles sink to the bottom over time and form a heavy powder. We emptied the pool again, and scraped the powder off the bottom (which when left in a bucket, sets quite firm) and gave it another good clean as the scale reformed, but not so thickly. This time I cleaned the top end with vinegar and the bottom with a diluted muratic acid wash and scrubbed it well. We then gave it a good blast with a high pressure water cleaner, and rinsed well will water. We partly filled the pool last night and added chlorine. The pH is 7.4 to 7.6 and the floating substance is back....overnight! The photos were taken this morning. I hope you can help us as we are at our wits end.
Pool details:
Inground concrete pool, fully tiled
45 000 gallons
Sand filter
We use red phenol and DPD tablets to test
It is slightly hard bore water which is drinkable.
It was previously run on a salt water chlorinator, but currently using chlorine powder and tablets.
There are no water features or spas.
Pool thread 2.jpgPool thread.jpgPool white clump 2.jpgPool White clump.jpg
 
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The powder reacts to acid - it fizzes.
Welcome to TFP! :wave: That appears to be calcium. Do you fill from a well or is your local city water very hard? That could also explain why you had to do a drain and acid wash previously.

How do you maintain your water chemistry? Do you have a good test kit?
 
Welcome to TFP! :wave: That appears to be calcium. Do you fill from a well or is your local city water very hard? That could also explain why you had to do a drain and acid wash previously.

How do you maintain your water chemistry? Do you have a good test kit?
Hi, We live in Portugal and we use bore water from the aquifer. It is of very good quality and drinkable, but is a little hard. My husband uses red phenol and DPD tablets to test for pH and chlorine. We are manually dosing powder chlorine for now.
 
My husband uses red phenol and DPD tablets to test for pH and chlorine. We are manually dosing powder chlorine for now.
That sounds reasonable since I suspect obtaining other testing products may be difficult in your area. Does he have anything to test CH levels? If not, it may be worth trying to obtain a good CH drop test kit. I don't know if you have any local stores to assist or if you have shipping restrictions to Portugal.
 
That sounds reasonable since I suspect obtaining other testing products may be difficult in your area. Does he have anything to test CH levels? If not, it may be worth trying to obtain a good CH drop test kit. I don't know if you have any local stores to assist or if you have shipping restrictions to Portugal.
Yes, he was saying he needs a better testing kit. Will try to get one. Thanks. We are a little confused as to why when the floating substance is rolled between our fingers it turns string like. Is this the way calcium behaves?
 
OK -- dichlor. Adds equal amounts of CYA and chlorine.

Your chemistry (TA and pH) must be relatively high to support calcium scale to float around in the pool. The way it acts between your fingers is from something else - a polymer or surfactant of some kind - that is binding it together. I suspect your pool guy adds some kind of algaecide or clarifier or whatever that is causing it.
 
OK -- dichlor. Adds equal amounts of CYA and chlorine.

Your chemistry (TA and pH) must be relatively high to support calcium scale to float around in the pool. The way it acts between your fingers is from something else - a polymer or surfactant of some kind - that is binding it together. I suspect your pool guy adds some kind of algaecide or clarifier or whatever that is causing it.
The pH is coming in at 7.4 to 7.6. We totally scrubbed the pool yesterday and refilled it partly last night and the surface has the floating powder on it again. When we had this last time, before we drained the pool the second time, it rained and the powder sank to the bottom. We really don't have a pool guy that comes regularly. He came out just once to fix the pool lights. My husband has been looking after it, and all was going well until we did the acid clean.
 
OK -- dichlor. Adds equal amounts of CYA and chlorine.

Your chemistry (TA and pH) must be relatively high to support calcium scale to float around in the pool. The way it acts between your fingers is from something else - a polymer or surfactant of some kind - that is binding it together. I suspect your pool guy adds some kind of algaecide or clarifier or whatever that is causing it.
We added flock to the pool before the first drain, to see if the floating powder would drop. It didn't.
 

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So it was something to do with the acid clean. What did they use to neutralize it?

Floc. Residual is likely the issue. Never use Floc,
 
OK -- dichlor. Adds equal amounts of CYA and chlorine.

Your chemistry (TA and pH) must be relatively high to support calcium scale to float around in the pool. The way it acts between your fingers is from something else - a polymer or surfactant of some kind - that is binding it together. I suspect your pool guy adds some kind of algaecide or clarifier or whatever that is causing it.
Also, after I cleaned the pool yesterday, using diluted muratic acid, little calcium nodules started forming very quickly on the grout at the bottom of the pool. They formed little pyramids growing within minutes.
 
 
I am actually wondering if we don't have two problems. We suspected white water mold, but on maturing the floating stuff becomes bigger. It's fine like talcom powder at the beginning then becomes grainy and gritty. Does anyone know how white water mold behaves?
 
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