White/gray powder precipitating out on bottom of pool

[leaky]

I have a very fine powder on the bottom of my pool. When I vacuum, it is so fine that it passes right through the sand filter and comes back in the pool. When I brush it, it clouds up quickly and eventually re-settles. Otherwise water is clear.

I have been vacuuming to waste and refilling, but it comes back. When I added a lot of water at the start of the year, the dust didn't appear until just now (late June).

The pool water tests OK, and they said I needed to increase calcium hardness, so I didn't think it was a calcium dust, but....?

I chlorinate with trichlor tabs and shock with leslies power powder pro.

I added some pH up the other night, and it seemed to get worse right then, but that could be coincidence..

Perhaps I should switch to liquid and/or a different shock?

Partially drain and refill?

Too much dissolved solids?

Thanks,

 

[JasonLion]

That sounds like calcium clouding. Power Powder Pro adds calcium and if calcium gets too high it can do things like that. If you post a complete set of water test results we can confirm if this is the problem and tell you what you need to do about it.

 

[leaky]

My wife took a water sample in, but didn't record the results. The guy tested "all 9 chemicals" and they were all good. He gave her a flocculent.... but the water is not cloudy...

I'll get the actual #'s, but the recent test was:

3 free chlorine
3 total chlorin
7.4 ph
140 TA
30 CYA
100 Calcium hardness (they recommend adding and I added 1/3 of what they said...)
500 total dis solids
0 phosphates

I will vacuum to waste and capture some of the dust - I'll add acid to it and see if it reacts....

Thanks

 

[JasonLion]

It looks like I was wrong. With those numbers there really isn't any chance of calcium clouding. Your TA is a little higher than ideal, but not enough to be an issue. Other than that everything looks great.

What kind of pool do you have (plaster, vinyl, fiberglass)? And if plaster, how old is the plaster?

 

[Freelancer]

I have just taken on a number of plaster pools from another company and all the pools (communal) are showing exactly what you have described. If your pool is not a plaster pool then this information will be of little use to you as vinyl pools care not whether you have calcium or not.

I did a water balance test and all pools again were out of balance on the acidic side of things. CSI -0.70 to -1.75 The problem was that the calcium levels were too low all around the 100 PPM some as low as 55 PPM, so I put calcium chloride in all the pools. Whilst the amount of dust has slightly decreased the damage to the grout in all the pools is so severe I cannot undo the damage caused and all the pools will need to be drained, tiles refitted where they have lifted and the pools re-grouted. Of course the whole water balance or lack of was not solely down to the calcium levels but also the high CYA levels, a quick drain of around 50% brought all the pools down to a manageable level of around 60 - 70 PPM. I would have preferred lower but installing automatic chlorinators ensures that I can assure adequate sanitization levels.

What I have noticed is that low calcium waters will leech as much calcium from the grout as it can, during this process and especially in pools where poor quality grout has been used the grout work will very quickly turn to power and sit on the pool bottom and tiles will start to detach from the pool. Once that has happened no matter how well you get the water back into balance the damage is done and the best you can hope for is to slowdown of the process. I find that maintaining my calcium levels as per the pool calculator @ 300 PPM and my CYA at 40 - 50 PPM prevents this from happening. Provided these two aspects are pretty much nailed the other aspects of the water balance are far more easily managed and will only effect the balance slightly before needing correction.

What is interesting is that all the pools I got the grout work was less than one year old in all the pools. So the damage can happen very quickly.

Looking at your figures if you increase your calcium to 300 PPM and reduce your Alk to around 90 your water would be near perfect balance. If you have a plaster pool I suspect that at some point your pool has been out of balance and what you are seeing is the result of damaged grout. Try brushing your walls and pool floor to see if you get clouds of powder, if so you can be pretty certain it's the grout you are seeing on the pool floor.

Of course if you have a vinyl pool then none of this is relevant and maybe someone with a vinyl pool will know the answer.

 

[leaky]

Thanks for the help so far... I have a vinyl pool. I vacuumed to waste when I had a lot of this stuff and put the discharge hose in a pail - see the dust that I collected. It is a very fine dust. I added some acid to the dust and it bubbled and dissolved it. See pictures of the dust, acid, and beginning of the collection of more of this on the bottom of the pool.

I do have well water, but fill through a softener. Perhaps some mineral that has accumulated...

I'm switching to liquid chlorine on the assumption that Calcium Hypo chlorinator might be at fault...

 

[josta]

I've got the same problem; white mush on the bottom of the pool especially in the jacuzzi, that turns into white powder when dry. Putting acid on the dry powder causes it to bubble.

FAC 3.0
pH 7.9
TA 130
CYA 60
CH 160
TDS 3300
Salt 3100

Is the CYA low enough to cause problems? I usually scoop out maybe half a cup a week from the jacuzzi. Brushing the walls of the pool does not seem to generate any clouds of powder, only in the jacuzzi, which is adjacent to and part of the pool.

John

 

[josta]

Any answers?

 

[chem geek]

josta,

With your numbers and using a hot spa temperature (100+), the CSI is around +0.2. Though not that high, I suspect that with the TA at 130 ppm that the spa pH rises quickly with aeration from spa jets so might be getting to 8.2 at which point you can get significant calcium carbonate precipitate. At a pH of 8.2, temp of 104ºF, and with your other numbers, the CSI is around +0.5 and the Calcium Carbonate Precipitation Potential is 9.7 ppm. In a 350 gallon spa, that would be up to 12.8 grams (about 1/2 ounce) of calcium carbonate -- perhaps 1-2 teaspoons. You are seeing around 4 ounces a week so around 3-1/2 teaspoons per day so perhaps your spa is larger than I assumed or you've got significant water exchange between your spa and pool daily.

Even in the pool I suspect your pH is rising too quickly due to the high TA and having a saltwater chlorine generator. The solution would be to significantly lower the TA. If you need to lower it to 70 ppm to get to pH stability and if your pool is plaster, then you'll need to raise the Calcium Hardness (CH) to protect that surface.

Richard

 

[josta]

We have not been using the spa much since it's been summer. The water is shared between the spa and the pool daily; the spa "overflows" into the pool.

Does the calcium precipitation hurt anything?

Ok, I'll try lowering the TA and raising the CH, thanks Richard!

John