Dirt or dead algae?

[Enumjon]

Last week all was well in the pool. Sunday morning when I took the solar cover off it looked like a bucket of dirt had been thrown in the pool and scattered around. A strange brownish/black dirt that looked like pond slime. But a light brushing and it disappeared. It has continued to return each day. Pool has also been more cloudy than normal. Picture are included - they were taken just last night, it was worse earlier in the week. My original thought was dead algae, but I am not convinced for a few reasons I will give below.

Bit of history. 2 weeks ago the pump impeller came loose and I did not realize it, so no water was being pumped for 1-2 days. Once it came up and running again a little green came out of the returns. Pumped up the chlorine level, and everything seemed fine for a week. Other changes? Our weather has become more cloudy and cool, pool temp has dropped from 88 to 82. We have been getting a bit of wind which will blow in dirt and pine needles, but no more wind than normal. Starting to get summer thunderstorms and rain. Cover is staying on more, but still coming off almost daily. Added dry acid rather than MA to lower pH one time. Everything else has stayed the same.

Strange things about the "dirt". It accumulates while the pump is running. It accumulates in front of return jets, not in dead spots. It is there in the afternoon when the pump has been running all day. Run the robot in the evening, and there is no "dirt" in the morning. Light brush and it disappears into the water, and does not re-deposit even after hours of no pool circulation. I have not felt it, too deep to reach without jumping in. Dumped in a bunch of chlorine a few days ago to do an ocult test. Not up to slam levels, but pretty high. Had zero loss of chlorine overnight, and only 1.5 loss the following day (went from 15 to 13.5). Have not had any CC the entire year. Overall pool levels have been steady through the whole episode, and about the same as prior to the dirt. Levels last Sunday were:

FC 6
CC 0
pH 7.2
TA 190
CH 550
CYA 60

I know that chlorine level was a bit low, so I have been keeping it higher this week. So my big question - is there an algae bloom going on that I need to slam? If so, why no chlorine loss? And I thought dead algae was light and settled later on, not while the pump is running right in the highest water flow areas. You advice is appreciated - as always.

 

[Enumjon]

Oh, one other potential source I did not talk about. My sand filter seems to be working fine. Pressure has been staying about normal, backwash every week or so when the pressure rises. The plumbing does not allow me access to look inside, I need to change the plumbing to be able to do a deep clean. I add a bit of DE generally, but have not this week since I don't want to plug up the filter when I am at work.

 

[Texas Splash]

Hard to tell from the pics, but at first glance it looks like algae. It's reassuring that you are passing an OCLT and have very little FC loss on a normal day, but it still would be good to try and capture some of that materiel. Since that stuff doesn't seem to be effecting your FC and is only falling under the return jets, I am suspicious about the filter. Is there any chance you could affix a sock to one of the return jets to grab some? Either way I see one of two things that may happen: Either you open the filter (which means re-doing the PVC) so you can do a deep clean. You may even have to empty it to inspect the laterals. Or, you run a SLAM Process hoping that it's just algae and not something physically wrong with filter. But at some point you'll just have to make it a DIY project and open-up that filter. That will be inevitable I'm afraid. But once you do it and reinstall everything with unions, you'll be in much better shape for the future.

 

[duraleigh]

It's algae. Regardless of whether or not you have chlorine loss, it is still algae............SLAM the pool.

You may or may not have a clogged filter. What is your current psi? What is your clean psi?

A CYA of 60 suggests a SLAM value of about 24, I think. Vacuum and brush daily, run the pump 24/7. The "dust" will get less and less each day if you follow the SLAM instructions perfectly.

You will need to SLAM the pool regardless but your psi may tell us if you need to deep clean as well.

 

[Enumjon]

When you say put a sock over the return - do you mean a skimmer basket sock, or a gym sock? I have been wanting to install unions to get at the filter, and just finished an irrigation repair so I have the stuff I need on hand - except the unions.

I backwash when the psi gets up to 20, psi of 17 after backwashing.

I will start the slam today - I figured that would be the advice. I was waiting until I had a weekend to devote to it. Once the slam is over I will install unions and dig into the filter. When you say put a sock over the return - do you mean a skimmer basket sock, or a gym sock? Thanks for the help!

 

[Enumjon]

Silly question on the slam - never done one before. Is it OK to have the solar cover on most of the time? I know that I need to remove it to brush a few times a day, but would like to be able to keep the heat and chlorine in as much as possible.

 

[Texas Splash]

When you say put a sock over the return - do you mean a skimmer basket sock, or a gym sock?

I was referring to a sock that you can place of the return jets to try and grab some of it since you said you couldn't get all the way in the water and the debris seems to be falling down under the jets themselves. Best to leave the cover off during the SLAM so the sun can oxidize any CCs in the water. Don't forget to lower your pH to 7.2 before increasing the FC to 24. Good luck!

 

[Enumjon]

Thanks for the pH info - I had just texted my son to start slamming the pool! Our pH needs to be dropped a little first.

 

[Enumjon]

Follow up on the slam. The pool is sparkling! Started the slam on Friday about lunch. Saturday morning the pool almost passed the ocult test - cc was 1.0. Besides, I figured that was too short a time even if it did pass, so I went one more day. Sunday morning it passed the test with flying colors - cc of 0. Since starting the slam no black "dirt" coming out of the returns. Also needed to use very little bleach - once I got up to slam level it only took about a gallon a day to keep it there, indicating very little algae was present.

My theory as to what was happening -I had an algae build up not in the pool, but somewhere in the equipment or pipes. That is why testing the pool water it seemed fine. Ocult test was just testing pool water, and that is not where the algae was located. This is also why the black stuff was getting ejected into the pool, chlorine was killing the algae and spewing their little carcasses into the pool. Thanks again for the help!

 

[mknauss]

Sunday morning it passed the test with flying colors - cc of 0

What was the Overnight Chlorine Loss Test result? FC loss of ???

 

[Enumjon]

First and second night chlorine loss was 0

 

[Enumjon]

And the pool was clear the first evening, but even more clear the second evening.

 

[Enumjon]

Here is the pool now - deep end is 9 feet.

 

[Enumjon]

Follow up question for the experts - based on the above picture. When I moved in I assumed that the blue color of the plaster was a paint or dye that was put there on purpose. But as I am currently fixing small dark copper spots - could that overall lovely blue color be due to copper staining? You can now see swirls of blue and swirls of white, the acid treatment for the copper spots also seems to be removing the blue coloring.

 

[duraleigh]

The blue color was in the plaster. We would all be multimillionaires if we could make copper "stain" that evenly.

BTW, are those plaster walls or some type of fiberglass panel?

 

[mknauss]

Copper stains are normally brown to near black. Not blue.

I suspect if you are doing some kind of acid treatments directly on the plaster, it is removing the top layer of the plaster. Copper stains are removed by using sulfamic acid and then the pool is drained to remove the copper from the pool.

 

[Enumjon]

The walls are plaster. The pool robot seems to be gradually removing the blue color, the dry acid in a sock copper stain removal just seems to be speeding up the process. Lesson learned - when the plaster needs a resurface do not add color to the plaster.