Help identify what's in my pool - beginning a SLAM

pfitz4

Bronze Supporter
Feb 26, 2018
47
North Alabama
Good morning! Proud to be a new TFP supporter.

Opened the pool a couple of weeks ago. Last week a fine sediment started appearing all over the pool floor in small patches and along seams of the vinyl liner. I assumed it was dead algae or pollen (we do have a ton of pollen in our area right now). I've tried brushing, vacuuming to waste and it returns the same day. It is tan colored and appears very dusty - it poofs and "disappears" when brushed. I know there are many types of algae and I've read about mustard algae. I've suspected it in past years but it's hard to know if this is a difficult algae problem, or just dirt/pollen. Is this how some types of algae behave? I've attached photos.

My pool seems to be consuming FC at a higher rate than normal. I haven't bumped CYA up yet since I want to clear this up first. OCLT last night showed a loss of .5. I plan to begin SLAM today.

FC 5.5 (this morning, was 6 last night)
CC 0
TA 70
CYA 30
pH 7.5
temp 70
salt 3200
 

Attachments

pfitz4

Bronze Supporter
Feb 26, 2018
47
North Alabama
Looks run of the mill algae. What you see is the dead algae.

SLAM away!
A few follow up questions.

Began slam today. FC consumption seems higher than I would expect. My DPD powder is clumpy - can that affect test results? New refills should arrive from TfTestKits tomorrow.

I am now wondering if my SWG is working properly, and maybe that’s why this problem arose in the first place. I replaced the salt cell last season. Thinking about doing a test of the SWG: set it to 100% overnight and compare FC results from night to morning. Like a reverse OCLT. Does this sound like a reasonable way to check the SWG? (will wait until after SLAM is complete to do this)

I know my CYA is low, and will raise once slam is complete. Can that cause FC to be used up rapidly, even this early in the season?
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
20,952
San Dimas, CA (LA County)
If the stuff on the floor looks like aquatic dustbunnies, it's algae.

Mustard algae grows on the shady side and it is the color of grey poupon mustard.

It's not uncommon for a pool with algae to use bleach almost as fast as you pour it in initially. I have no idea what you';re basing your expected consumption on. With low CYA, you'll lose a lot to sunlight, too.

Testing the SWG. Just set it to 100% and catch a sample at the return. It should be hiogher than the pool as a whole.
 

JamesW

TFP Expert
Mar 2, 2011
13,859
It might be mustard. A full SLAM should take care of it.

For the AquaRite, if the instant salinity reading in diagnostics is correct, then the cell is producing the correct amount of chlorine.
 

pfitz4

Bronze Supporter
Feb 26, 2018
47
North Alabama
Thanks for the tips on SWG.

I would describe the stuff as being tan or brownish yellow. Not green. Not gray. Scatters/poofs immediately. Strange to me that the water is crystal sparkly clear otherwise...

I will keep FC at SLAM level all day tomorrow then do OCLT and post results. Should I raise to mustard level after completing the slam, just in case? Any downside to this? I do worry about bleaching the liner.
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
20,952
San Dimas, CA (LA County)
Thanks for the tips on SWG.

I would describe the stuff as being tan or brownish yellow. Not green. Not gray. Scatters/poofs immediately. Strange to me that the water is crystal sparkly clear otherwise...

I will keep FC at SLAM level all day tomorrow then do OCLT and post results. Should I raise to mustard level after completing the slam, just in case? Any downside to this? I do worry about bleaching the liner.
If that dead algae keeps clumping, then the water is not clear, and it would be premature to run the OCLT.

Raising to Mustard levels is probably still lower hypochlorite ions than 2 or 3 FC ppm with no CYA, which is the standard for commercial pools. Shouldn't affect the liner at all, just be patient when adding bleach. Dribble, don't dump it into the return stream.
 

pfitz4

Bronze Supporter
Feb 26, 2018
47
North Alabama
If that dead algae keeps clumping, then the water is not clear, and it would be premature to run the OCLT.
Makes sense. I am still seeing clumps of the sediment all over the pool floor this morning. Less than before. I would describe it as dust piles. Still golden brown in color. Do I wait until it is brushed/filtered out? Or do I vacuum and see if it returns?
 

aeh0603

Well-known member
Apr 6, 2016
155
San Diego, CA
The "dust piles" on the bottom of your pool are most likely dead algae. It means you need to keep SLAMing to get rid of the algae. As for removal, vacuuming will be the fastest way to remove it. If it returns it means you are still killing algae in your water and you need to keep SLAMing.
 

pfitz4

Bronze Supporter
Feb 26, 2018
47
North Alabama
Everything is looking good! Thanks for all the help. Water is sparkly clear, and I only see very small trace amounts of the dusty stuff (hopefully the dead algae). I will keep at SLAM level for another day and then do OCLT.

Question about when to bring CYA up to appropriate level. Should I first allow FC to drift down to normal level? I don't want to risk seeing the dusty dead algae come back having to SLAM again at the much higher FC levels.
 

JamesW

TFP Expert
Mar 2, 2011
13,859
Once the SLAM is over, you can raise the cyanuric acid level.

I would recommend that you maintain an elevated fc/cya ratio of 15 to 20% for a week after the SLAM is complete just to be sure that the algae does not return.
 
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Teald024

TFP Guide
Don't rush towards the OCLT. Continue the SLAM process until the water is clear (including no dusty stuff on the bottom). Then you can run the OCLT.

Once the SLAM is complete, then you can add CYA. FC doesn't need to drift down first. Then keep FC at an appropriate level for the new CYA level.
 

pfitz4

Bronze Supporter
Feb 26, 2018
47
North Alabama
Alright. Passed OCLT for two nights in a row. Water sparkly even after rain over the weekend. Now I’m back to having my pump on timer mode - running 10 hrs/day with SWG set to 50%, which is my typical setting during the summer. I was surprised that FC already drifted from 12 down to 9 over the weekend. I guess the loss is a result of the low CYA?

I collected a sample from the return to see if the FC is higher when the SWG is set to 100%, as advised earlier in this thread. I got the same FC result of 9. Any other way to make sure my salt cell is generating chlorine adequately?

FC 9
CC 0
Ph 7.5
TA 70
CYA 30
 

Flying Tivo

Well-known member
Jan 24, 2017
666
Monterrey, NL, Mexico
Try running your pump 5 hrs a day with your SWG at 100%, you will save some money. Yes your low CYA will burn your extra FC fast. Try to raise it to around 70, do it in batches so you dont overshoot.
 

JamesW

TFP Expert
Mar 2, 2011
13,859
Ok, those numbers look good.

The most important number is the instant salinity. As long as the instant salinity is accurate, the cell is working properly.

Be extra vigilant about the fc because that type of algae can be persistent.

I would maintain a fc/cya ratio of 15% for a week just to be safe.
 
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