Greyish powder on pool bottom. Algae or something else.

[Gbick]

Hey everybody. New guy here. Sorry for the long post but I’m at a loss. I’ve read several threads similar to this but never figured out what this grey powder could be if it’s not algae. I’ve fought this on and off, mostly on, for 5 or so years. This grey powder shows up on the bottom of my pool and after I vacuum on waste it always comes back, usually by the next day.

About 3 years ago I decided it was mustard algae, started reading this forum and determined my CYA was too high, around 110-120, and likely the problem. I was brushing the pool after dark every night and keeping the chlorine super high with bleach all while gradually lowering the CYA by draining water and it still kept coming back. Eventually after getting the CYA down around 70 my wife tired of the whole process and started using something called algae complete, which I know you guys don’t recommend, but it seemed to work. Everything has been fine the last couple years until this year it’s come back again even with the algae complete. Based on a faulty reading at a pool store I ADDED CYA because it was supposedly low. So it wound up back in the 110-120 range again. I’ve gradually gotten it down to about 80 as of today.

I’m still not 100% convinced it’s algae though. It’s only on the bottom of the pool, not the sides and doesn’t really “cling” to anything but it does disappear into a cloud of dust if you brush it and eventually resettles. Also the water is perfectly clear. Several months ago we had vacuumed it to waste and with a few hours there were some small spots right around the edges where the jets blow. So I turned off the pump and let it sit for a few days. Nothing else showed up. Two days later I turned the pump back on and it began to accumulate again. So this sounds more like a filtration issue or something being pumped in, right?

I finally got so frustrated that I called a pool company and the owner immediately said it was dead algae. We figured it was not being filtered out effectively so we changed the sand in the filter, which I also know is not recommended but I figured it wasn’t gonna hurt and would at least take that out of the equation. They also verified none of the laterals were broken. Well after several months of very questionably maintaining the pool and not getting rid of the problem the owner has come back out and decided it’s NOT algae. He’s determined it’s some type of chemical fall out and speculating calcium. It’s a vinyl liner pool btw around 17,500 gallons. I just checked my reading today with the TFP test kit and got:
FC 11
CC .5
CH 125
CYA 80-90
TA 50
PH 7.5
So it doesn’t sound like it would be calcium. Oddly even when we’ve managed to get rid of the stuff every time we add balance pak 100/baking soda it seems like it comes back.

Was hoping someone here could tell me if this sounds like definitely algae or could it be something else, and if so, what?

Thanks

 

[mknauss]

Welcome to the forum.
Great decision to get a proper test kit.
First step is to do an Overnight Chlorine Loss Test

If it poofs away when you get near it, that is very likely dead algae.

Why are you adding baking soda?

 

[Gbick]

Welcome to the forum.
Great decision to get a proper test kit.
First step is to do an Overnight Chlorine Loss Test

If it poofs away when you get near it, that is very likely dead algae.

Why are you adding baking soda?

The baking soda was to raise total alkalinity based on pool store test results. It hasn’t been recently. I was just noting that it seems like every time I’ve added it I seem to get “algae” if that’s what it is. Wasn’t sure if the baking soda and the grey powder could be related. I’ve been thinking all along it’s dead algae but the fact that it only seems to accumulate when the pump is running doesn’t see to line up with that. Will definitely try the OCLT later this week when I can do it shortly after dark and early in the morning. I’m a musician so I have weird hours.

 

[Gbick]

Welcome to the forum.
Great decision to get a proper test kit.
First step is to do an Overnight Chlorine Loss Test

If it poofs away when you get near it, that is very likely dead algae.

Why are you adding baking soda?

Ok it took a while with my weird schedule but I finally got around to doing the OCLT and as far as I can tell I lost no chlorine. Yesterday, right around sunset, it took 17 drops so my FC should have been 8.5. This morning, about 12 hours later, it again took 17 drops. You could make an argument for 16 as it was mostly clear at 16 but completely clear after 17. So I either lost no chlorine or at most dropped from 8.5 to 8. I had no CC either time I tested it. So this should indicate it’s not algae, correct?

Also prior to this I had not been running the pool for 8-10 days as I had the water level a little low for someone to repair a crack in my steps. The grey powder was just sitting there the whole time. Not growing or expanding. Just sitting. As soon as I started running the pump again there was new darker brown stuff on top of where the grey stuff has been. I brushed the stuff up just to see what would happen and by the next day it was all back again. I’ve been suspecting this stuff only accumulates when the pump is running. So last night I brushed it again and attached white tube socks over the return jets and left it running all night. So far nothing has returned in 12 hours and I don’t think it’s going to. So doesn’t it sound like something very fine that isn’t algae is not being filtered out? Any ideas? Thanks for your help.

 

[Newdude]

Any ideas?

If you passed the OCLT (lost no FC overnight) then the debris you see is environmental. Whether it's dust or pollen or something else that's blowing in, it's blowing in. I had similar on both a heavily treed yard and now a wide open yard next to a farm.

If it takes 2 days to vac it off the floor, and day 3 is breezy again, it seems perpetual, but it does fluctuate and gets particulary worse in the spring and fall.

With knowledge that your pool has a near constant supply of crud dumping into it, ensuring your FC never goes near min is utterly critical.

(Assuming you have a SWG because the 70-80 CYA)

 

[mknauss]

Why are you adding baking soda?

 

[sande005]

You don't mention how you are routinely chlorinating - do you have a SWCG, only adding liquid, usings tabs?
With your CYA apparently bouncing around over the time periods, highly likely you were having high/very high periods where there was not near enough CL, and algae got a foothold.
Live algae tends to suspend in the water (until it grows so much to be see as green on the surfaces too). Dead settles out. Might it be a combination of having Cl added when the pump is running (which kills things and they drop out), but then it gets used up enough to allow it to again grow (which may not accumulate very much), until the next Cl/pump cycle?

Seems like too many things changing over time to track well.

Do a full on SLAM. Keep at it, monitoring for all three criteria - water clear, no change in the overnight test, NO sign of algae. Scrub everything well - sides, ladders, lights, etc.
It may take a week or more.

After, make sure you keep the Cl at 6-12 all the time, with your CYA 80-90 level. (I'd lean toward 10-12)
If you have a SWCG, and can slow down the pump, set things to run 24/7 at lower speed to greatly help in keeping the Cl level consistent.
If not, test a couple of times daily until you get a grasp of how much the Cl levels on your pool vary. Add Cl as needed after each test to keep it in the 6-12 range always.
This will vary as the seasons change, so better to test often than not enough.