White powdery deposit on pool floor

[paulkmoore]

Hi everyone,

I've just taken the winter cover off the pool to discover quite an amount of powdery white substance over the pool floor - please see photo.



Any ideas what this could be? It's a vinyl liner pool so it's not leached from the grout.

For context, I shocked (liquid chlorine) and added winterising algaecide to the pool as part of the close down at the end of last season. Possibly some reaction between the two?

Presumably I should just vacuum this to waste, but I read elsewhere on the forum that this can be related to a dirty filter.

Any thoughts / guidance welcomed.

Thanks

Paul

 

[JohnT]

Looks like something that blew or washed into the pool on the shallow end. Sand or soil?

 

[paulkmoore]

Thanks for the reply John but we are not coastal, and the powder is definitely pure white. It doesn't look like sand or soil to me.

 

[domct203]

Have you tried to retrieve any of it? How does it feel? Is it gritty, slimy, sticky etc?

A complete set of test results may offer clues as well.

Trying to identify it from a picture will be next to impossible.

 

[pooldv]

If you can gather some put some muriatic (hydrochloric) acid on it to see if it fizzles up and dissolves. Could be calcium scale, some prior test results will help confirm or deny this.

 

[paulkmoore]

Thanks domct203 and pooldv, I tested the water today, results below:

FC: 0.02
CC: 0.09 (basically no Chlorine - understandable given I've not added any this season yet)
PH: 7.4 (bit low but ok)
TA: 205 (fine)
CH: 210 (fine - see note below)
CYA: 28 (slightly lower than I'd normally maintain it - but again ok)
​

Broadly, these are as I would expect for a post winter pool.

My previous readings from last season are here:

Swimming Pool Data - Google Sheets​

I note that the CH increased at the tail end of last season and seems to have dropped off significantly (331 -> 210), so I suspect the precipitate is Calcium based.

@pooldv - I've ordered some muriatic acid - should be here on the 5/6th April, and have taken a sample from the pool floor today to dry it out in preparation for testing. Will report back further then.

@domct203 - the substance looks 'gritty' - very much like a solid in solution, as below:



Thanks

Paul

 

[duraleigh]

Since your Calcium dropped, it seems logical that you precipitated some out of solution over the winter.

How? Well, your TA is too high. You know your stuff so why do you think it is fine? 80 would be better. So, if you have, at some time over the winter, had your pH up too high as well, the calcium probably came out of solution.


About the only other explanation is someone put something in your pool that didn't belong there. It was not the algaecide. Can you think of anything else that got put in your pool?

Since the conditions that probably caused it were transient, I would vacuum it to waste and forget about it.

 

[paulkmoore]

Hi duraleigh, thanks for the response.

Regarding the TA level, I'd always considered that TA had to be >50 to offer reasonable PH buffering, but not that my levels were particularly high - so I've learned something here.

My PH levels were slightly high at the end of last season, so I suspect the high CH, high TA and high PH combined have caused the precipitation. I'll still do the test, now that I've ordered the muriatic acid

Looks like I also have some TA lowering work to do - thanks again for the tip.

Will vacuum to waste tomorrow.

Thanks, Paul

 

[pooldv]

Yes, the combo of high TA, CH and pH can certainly lead to calcium scaling. More here, Pool School - Calcium Scaling

Also here are the recommended levels for TA and others, Pool School - Recommended Levels

 

[paulkmoore]

Thanks @pooldv, very useful.

Interesting looking at the effect of the various levels on the CSI in the PoolMath calculator, thanks again.