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White Powder On Bottom Of Pool


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Hi. This is our first year with our 18 x 36 inground salt water pool. We have been on top of our pool chemistry all year and the results have been always bang on as has the water; clear and sparkling.

I brought a sample to get tested at our local pool place and the analysis showed a slightly high ph (which I knew from my home test kit but didn't get around to lowering it before bringing in the sample ... my mistake). The ph was at 7.8. They said that my water though was at a high saturation index and scaling would become a problem. 2.75 litres of a sequestering agent was advised for our 110,000 litre pool and off I left with a product called "Shield" made by Mursatt Chemicals (akin to Bioguard Pool Magnet).

My wife put in the "Shield" last evening and ever since, the water has been cloudy. I lowered the ph this morning and it is now at 7.4. Calcium hardness and total alkalinity are in the middle of the ideal range. Looking at my water this afternoon (some 16 hours later), I believe the water is clear but looks cloudy because there is a layer of a white powdery substance spread out evenly across the entire pool bottom ... both shallow and deep ends. I brushed it and it stirs up quite easily into a cloud which remains suspended. I put in the vacuum but the particles are too fine to be trapped so now the water is back to being completely cloudy.

Any idea on what this is? The pool "experts" don't have a clue. My guess is some type of reaction with the "Shield" and the minerals in the water ... maybe some type of oxidation reaction? Maybe too much "Shield" for the water chemistry? I believe I have some high iron or copper as my daughter's blond hair is turning slightly green although she basically resides in the pool. I'm hoping that the vacuum will stir up the powder for the skimmer to grab it and the sand filter to eliminate it but I am worried that the powder is too fine for even this to be successful. Other than this, I'm not quite sure how to get rid of it.

Any advice on what this is along with a cure would be greatly appreciated!

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It could be a calcium deposit. Also, have you thought about it being mustard algae? Probably not as those are often misdiagnosed, but it's a thought...

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I won't speculate as to the source of the mysterious white powder*, but don't try to stir it up. Throw a hose in the pool (not enough to reach the bottom, just a couple of inches underwater), raise the water level by 1-2" (will take a couple of hours for an 18x36), hook up the vac, unroll the backwash hose, set the multiport valve atop the filter to waste and turn the pump on. If you use a vacuum plate in the skimmer instead of inserting the end of the vac hose into the hole at the bottom of the skimmer box, then make sure the plate is secure. Then go back to your equipment pad and close the valve(s) controlling the main drain(s) to maximize vacuum suction. Then vacuum all that powder from the bottom and out to waste. Your water level should be good afterward as you raised it before vacuuming to waste, but work quickly and w/ a purpose while vacuuming.

I always vacuum to waste on those rare occasions when I find significant debris on the pool bottom. All things being equal, I'd rather eliminate it completely and keep it out of my filter, saving the need for backwashing and ensuring nothing gets through the sand and back into the pool. I hate doing things twice.

*OK, I'll speculate. Obviously something precipitated out of the water. You're right, Shield is a sequestering agent for copper - and you note your daughter's hair has turned slightly green. Have you ever used a copper-based algaecide, like BioGuard Banish? You're getting copper from somewhere - do you have a heater? How old? Perhaps corrosion in the heat exchanger? Anyway, if the product works your copper should be gone or mostly gone. Could calcium have somehow precipitated out? Perhaps. Anyway, vacuum to waste as outlined above and move on, hopefully you'll never have this problem again!

EDIT: just realized your post is nearly two months old. What did you do and is the problem solved?

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Thanks for the replies wifey and jkusmier.

jkusmier ... I did stir it up (prior to your post ... oops) and began noticing improvements slowly throughout the day yesterday. This morning when I looked at it, the water is about 90% - 95% clear and there was only about 5 very small deposits on the bottom of the shallow end. Yesterday, the entire pool bottom was covered; both in the shallow and deep ends. My belief is that the water was eventually able to absorb it as opposed to the filter trapping it. I backwashed prior to brushing and vacuuming the bottom and today, noticed that my psi did not change in my filter so therefore my assumption. The vacuum did a real good job of stirring it up as the product sifted right through the vacuum bag. Thanks for your comments on using the waste feature ... we were never told about it (along with many other things) and will definitely do it next time (if there is a next time).

I'm not sure if there is copper in the algaecide that I use but I will check later today. I'm thinking of shying away from the use of algaecides because of my salt water generator and it's ability to control that aspect. I've used 2 algaecides: Bioguard Polygard and Aquarius Algaecide (40%). Yes, I do use a heater (325000 btu Jandy Lite2) as I live in Canada but the summer has been gorgeous and the heater was mainly used in May and up until the middle of June. It will run sporadically throughout the night though ... this is Canada after all. The pool and heater is brand new so I hope it's not corrosion! The water is kept at 84 F.

My own belief is that calcium did precipate out of this. As I said in my first post a few months ago (different topic ... had to do with Bioguard Mineral Springs vs 'ordinary' pool salt), I have been trying to cut the umbilical cord from the pool dealer due to customer service and pricing issues. I've had great success keeping my water clear, clean and sparkling by going with the advice of friends with pools, what I read (here included), and my instincts as they improve. For some reason, I thought it prudent to have it checked at the dealer knowing that the analysis will suggest spending $50 - $100. So, the analysis showed all important levels in the middle of the ideal range although calcium hardness was slightly elevated at 190. Saturation and scaling was never really mentioned as something I should be concerned about so being a novice, I went with their advice.

Here is what I think. Their analysis showed a high saturation index (I don't have the exact number with me) but it wasn't extreme and that scaling could present itself. The recommendation was 2.75 litres of Bioguard Scale Inhibitor but having none in stock, they recommended the Mursatt Chemicals "Shield" product. They said and I quote ... "exact same thing as the Scale Inhibitor". Interestingly, the Bioguard Pool Magnet was also in stock but they suggested the Shield. Anyway, the Shield was added and the pool automatically reacted in a huge cloud. I checked the MSDS datasheets and I don't believe they are in fact the same thing, or at least, sold in the same concentrations. I believe I overwhelmed the pool with this product and the end result was cloudy water with the cloud settling into a white deposit on the bottom. I will take a water sample in today to compare calcium hardness levels.

I will let you know but thanks again for your well informed advice.

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You can get the saturation index (although possibly not calculated quite the same way) from the Pool Calculator. CH 190 is not high at all, in a salt pool it would be hard to be at risk for scaling at that level. But lowering pH is the easiest way to lower the saturation index; you didn't need whatever it is they gave you. (I found the MSDS for Shield and it is like the one for Pool Magnet but Mursatt adds sodium hydroxide; I don't know enough to say what that would do.)

I'm told green hair is from copper. HTH in particular has started putting copper in their chlorine products, if you use their chems then you might be adding copper without really being aware of it.

--paulr

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Just a quick update ...

The pool completely cleared in about 2 1/2 days. Once again ... clear and sparkling. The pool "experts" that we deal with have no clue what this white substance was but it was apparently absorbed by the water (with some help perhaps from the filter).

Ironically, their analysis of the water showed the exact same calcium hardness number (190) both before and after this episode. Two thoughts: the white powdery substance wasn't calcium (you would think there would be some variation) ... or ... their tests are not any more scientific than mine and they just threw out this number.

The only recommendation was to shock the pool because the total chlorine number (3) was not the same as the free chlorine (2). My comment to them was that instead of shocking, wouldn't it be wiser to kick up the swg a little bit. The confused look spoke volumes.

Thanks for everybody's replies.

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  • 9 years later...

I manage a pool company in Florida. I’ve had several pools that turn milky white and have heavy deposits of white powder resembling “flour” on every square inch with  heavier concentrations in the creases  24 hours after adding, on average , 10 pounds of alkalinity increaser along with 4 pounds of calcium increaser. I tested the backwash water for alkalinity level, tested 400 ppm, pool water tested at 120 ppm. Backwash water was pure white resembling milk. Vacuumed to waste/discharge, did a sand change and even a full filter replacement and the powder still returned. I’m at a loss, any advice would be great 

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First advice, start your own thread, don't hop on a 10 year old dead thread. Some site users might miss it, and you miss their advice.

High alkalinity will cause dissolved solids to come out of solution. Rapid ph and alkalinity changes cause temporary cloudiness. Calcium cannot dissolve into solution in high alkalinity. By adding these products at the same time in the same area you created a situation which prevents the calcium from remaining in solution in the water. Not sure if that is what is causing your issue. Pool chems are not my area of expertise.

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