Sandy feeling substance on sun shelf?

[RexO]

Hi All, I am a new, first time pool owner. The pool is 3 months old now. I clean and balance my pool meticulously, but only recently (2 weeks) found out about TFP and the saturation index. Yesterday, I noticed a sandy feeling substance on the sunshelf. I manually vacuumed the sun shelf and the entire pool surface, then brushed it this morning. I cleaned the filter today and noticed a fair amount of what looks like white beach sand. We live 10 minutes from the beach but have not been there in a while, so it is not beach sand. And, the substance was actually whiter than our East Coast, FL beach sand. I am wondering, what it could be?

I have been keeping the pool pH at the range of 7.6 - 7.8. For sure it has seen 8.0 at times. I am currently sitting at pH 7.6, Alkalinity 70, CYA 50 (I know, low for a SWCG pool), FC 4, No CC, calcium hardness 360, Salt 3400. Testing with Taylor 2006C and K1766.

More background. Pool details are in my signature, but can briefly re-cap. 10K gallons, exposed aggregate (Freestone, with a bright blue color plaster, iChlor30 SWCG, AquaCal, Heater, 1 HP Pentair VSP. The builder used a sequestration agent at start-up. I had my Phospates checked by the pool store, they found phosphates to be 1000. We presumed it was from sequestration agent since the fill water showed no phosphates. I discontinued the maintenance dose of the sequestration agent and tried a No-Clouding Phosphate treatment. I followed the instructions on the label but the product did not work. Still 1000. Then, I did some internet research and tried Orenda PR-10000, 8 oz. Knocked the phosphate from 1000 to zero with one treatment. I understand phosphates don’t necessarily need to be treated, but I still prefer not to carry the 1000 ppm load if I can use a 1-time treatment.

So, what do you think the sandy substance is from? Could it be calcium coming our of solution after discontinuing the sequestration agent? Or, could it be salt coming our of solution? I added one bag of salt one month ago, thats it. My pool store readings on Salt have been 2800 -3400. I used the K1766 for the first time today (just received it) and confirmed 3400. Over the last week I drained about 3 inches of pool water because of heavy rains. The pool is still filled a little on the high side because of the rain. That’s why the CYA is low. I was expecting the salt to show a bit lower because of diluting, but it is still holding on the high end.

I know....long post. Any ideas?

Thanks,
Rex/

 

[Texas Splash]

Rex, I suppose the first thing we need to do is try to determine what exactly is that substance on the sun shelf. Are you only seeing it on the shelf Are there any return jets near that shelf? I doubt the sequestraunt has anything to do with it, nor the phosphate issue. This sand feeling, it brushes away right? It's not there permanently? Are you able to collect any of it?

 

[RexO]

Thanks for the reply.
There is one return over the sun shelf. The sandy substance did just vacuum up. I id not feel it on the surface anywhere else as I survey the shallow end of the pool. I just checked the sunshelf and it is still sand-free. I went back over to the where I wash out the filter and collected some of the substance. It literally looks and feels like sand. See picture attached. We have had plenty of rain in the last few days and I have skimmed out some leaves. But, that is pretty much a regular thing. Just never found the sand in the pool. Maybe I am just over-thinking it. Thanks again,

 

[RexO]

Thanks for the reply.
There is one return over the sun shelf. The sandy substance did just vacuum up. I id not feel it on the surface anywhere else as I survey the shallow end of the pool. I just checked the sunshelf and it is still sand-free. I went back over to the where I wash out the filter and collected some of the substance. It literally looks and feels like sand. See picture attached. We have had plenty of rain in the last few days and I have skimmed out some leaves. But, that is pretty much a regular thing. Just never found the sand in the pool. Maybe I am just over-thinking it. Thanks again,

Or,

Thanks for the reply.
There is one return over the sun shelf. The sandy substance did just vacuum up. I id not feel it on the surface anywhere else as I survey the shallow end of the pool. I just checked the sunshelf and it is still sand-free. I went back over to the where I wash out the filter and collected some of the substance. It literally looks and feels like sand. See picture attached. We have had plenty of rain in the last few days and I have skimmed out some leaves. But, that is pretty much a regular thing. Just never found the sand in the pool. Maybe I am just over-thinking it. Thanks again,

Or, could it be salt coming out of solution over the sunshelf because of the warm water?

 

[Kevmartin01]

This is coming from a total noob but, I see in the second picture that you have brick pavers. Could the rain have washed some of that sand on to the shelf?

 

[Randrx2]

I vote paver sand.

 

[RexO]

I vote paver sand.

But I have a concrete deck. The pavers are on the side of my house where I clean the filter. And no sand in those pavers except the stuff I washed out of the filter.

 

[kellyfair]

Is your soil sandy? Asking because mine is, and if I had an in-ground pool and really rainy weather (looks like it is going to be a wet weekend, by the way) I would immediate assume runoff from the rain.

 

[Randrx2]

But I have a concrete deck. The pavers are on the side of my house where I clean the filter. And no sand in those pavers except the stuff I washed out of the filter.

That is strange. Maybe the substance in your hands came from the hose kicking up sand in the pavers? Are you saying there is no sand in the pavers in your picture? Could it have gotten blown or tracked in somehow?

 

[Randrx2]

I also just noticed your pool is open with no screen. It could be sand/dirt blowing in. Do you have a return on your sunshelf? If there is not a strong return there, it seems that the water would not circulate as much and the sand would accumulate there.

 

[RexO]

That is strange. Maybe the substance in your hands came from the hose kicking up sand in the pavers? Are you saying there is no sand in the pavers in your picture? Could it have gotten blown or tracked in somehow?

I probably threw people off by taking the pictures by the pavers on the side of my house where I cleaned the filter. I have not added any sand to the pavers since they were initially laid years ago. The sand on and in the pavers came from my filter when I washed them.

 

[RexO]

I also just noticed your pool is open with no screen. It could be sand/dirt blowing in. Do you have a return on your sunshelf? If there is not a strong return there, it seems that the water would not circulate as much and the sand would accumulate there.

You all just helped me figure this out. The sand is not from my house. I just remembered. My neighbors just had a new paver deck installed and of course it must still be very sandy. Guessing there young girls were over for a visit when I was not home. Probably played on the sun shelf after walking over barefoot. Should have thought of that sooner.

 

[RexO]

Is your soil sandy? Asking because mine is, and if I had an in-ground pool and really rainy weather (looks like it is going to be a wet weekend, by the way) I would immediate assume runoff from the rain.

Thanks Kelly. I do get some leaves on the deck and the pool but I have not seen sand. I am thinking out the neighbor girls with a new "sandy" paver deck probably tracked some sand over.

 

[Randrx2]

You all just helped me figure this out. The sand is not from my house. I just remembered. My neighbors just had a new paver deck installed and of course it must still be very sandy. Guessing there young girls were over for a visit when I was not home. Probably played on the sun shelf after walking over barefoot. Should have thought of that sooner.

That’s some nice sleuthing!