White dust on pool floor?

cesmode

Well-known member
Jun 9, 2017
53
Hackettstown
Hi,
I had an inground pool put in 3+ yrs ago.
In ground vinyl liner 16x34
Pentair FNS plus 48 DE Filter
I have a chlorinator that I keep on a low to medium setting. I drop in liquid chlorine once every few days.

Current Chems: (taylor test kit)
FC: 5.5 - 6
TC > .5
PH 7.3 to 7.4
TA - 75-85
CH - 75-85
CYA 60-70 ** I know its a bit high, working on it.

Water is crystal clear and always has been. Never have a problem with cloudy water or algae in the pool. I brush the walls once per week. I use bioguard algeacide once per week.
I backwashed my filter a few days after July 15 and then again on July 29. Both times I took the actual filter out and hosed it down as well. I did notice a possible small tear on one of the filter sheets toward the bottom. The rest are in great condition.

Before the July 29 backwash through today I have noticed white streaks of dust on the pool floor. They seem to settle in the seams of the vinyl liner as well as slope/deep end. They are easily disturbed and kicked up. My dophine vacuum bot vacuums it up. When I clean the bot, it really looks like sand or something. My wife is very concerned that it is DE (she even made a forum post on a neighborhood facebook page and everyone said its a bad filter/DE coming into the pool). I am not convinced that it is, even with the small tear. I don't ever see anything other than water and bubbles coming from the returns. My FC remains high, my CC remains low. Everything else is great IMO.

Any thoughts as to what this white dust can be and how can I get rid of it permanently? As mentioned, Im using my vacuum bot to suck it up (Im not vaccing to the filter). And it appears every morning (I run the filter at night).
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,031
Laughlin, NV
Can you pick some of it up? Smear it on a paper towel. If white/gray, it is DE. If greenish/yellow, it is algae.
 

cesmode

Well-known member
Jun 9, 2017
53
Hackettstown
Im unable to pick it up. It disappates/disperses when I try to.

Chem levels look OK, not a spot of green anywhere in the pool.

As far as DE...if it is infact DE, what could be the cause? The smallest tear? And would it continue to shoot DE back into the pool until I replace the sheet? I thought DE is more creamy when wet than fine and dusty.

Ive also read that it could be the multiport valve...is that the valve that handles back wash vs filter vs recirculate vs close vs winterize? Or the other one that closes returns and such?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,031
Laughlin, NV
A tear in the filter grid could easily let DE into the pool.

The MPV is the one you use to select Backwash, Filter, etc.
 

cesmode

Well-known member
Jun 9, 2017
53
Hackettstown
Hi,
Update:

To start and for comparisons purposes, when dealing with this white pool dust, Ive had my bot vac it all up. When it was done, I took a look at the little filter boxes inside, and it really looked like sand...rough sand. Not like DE.

I hosed down the filter a little bit yesterday (not fully) just to get a better look at the grids to see of there were any tears or rips. I even had my wife take a look for a second pair of eyes. We did not see anything . We had THOUGHT we saw a tear a week or two ago when I had hosed down the filter, so we remember what we saw being in a visible area toward the bottom of one of the grids, not tucked away in some crevice. So...we didnt see a tear.

I put the grids back into the filter. Backwashed. Then set the mpv to filter, and out comes the DE. I understand WHY this happened, but this has never happened to me in the 3+ yrs of doing this. Long ago, I think possibly somewhere on these forums because I come here for a lot of good information, someone had said to reverse the flow back and forth a few times between backwash and filter to really knock the crud off. I do that every time I backwash and nothing has ever come back into the pool. Ever. Except this time... Finishing it off, I added slightly less DE than I normally do.

Sooo, The water was cloudy. I dropped my pool bot in. When he was done, he vacc'd up all the DE. Now THIS was DE as opposed to what I described at the start of this post. This stuff was caked onto the sides of the filter boxes, all creamy, just like you would find in your pool filter. It did not resemble the sand stuff Ive been vaccing up for two weeks.

So I have my bot doing its thing again this morning because theres more stuff at the bottom of the pool after the filter ran all night. I'll keep doing this for a few days and see how it goes.

When I get home this evening Im going to do a full chem check. My wife wants to bring in someone who services pools. We have maybe 3-4 weeks left of the season, Id rather not drop 300-500 dollars right now.

Any thoughts?
 
Last edited:

cesmode

Well-known member
Jun 9, 2017
53
Hackettstown
What I am planning to do in the next day or two:
Check the filter basket o-ring for quality,make sure its lubed, make sure that it sits in the groove correctly and that we get a good solid seal.
I'll unscrew the MPV to see if I see any cracks.
Ill unscrew the diverter valve to see if there are any cracks and to make sure that the handle is in the correct position and wasnt bumped out of alignment

Anything else?
 

cesmode

Well-known member
Jun 9, 2017
53
Hackettstown
Update:
I opened up the MPV. Nothing looked cracked, everything looked fairly new as I would expect for a 3 yr old pool. I didnt see an oring...just the spider gasket. Gave that some lube. The valve seemed to turn a bit easier, hopefully sealing better? Could this help?
Gave the pump basket oring some lube, that had a tighter seal than before.

Anyone have any thoughts on this?
 

cesmode

Well-known member
Jun 9, 2017
53
Hackettstown
Replaced a grid that had a cracked plastic rib. Inspected all other grids twice. I had 3 sets of eyes look at the manifold, no cracks. Still having the issue.