Completed SLAM last week and now yellowish/brown stuff

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C

CharlyT

Member
Jun 2, 2023
7
Houston, TX
Pool Size
2900
Surface
Vinyl
Chlorine
Liquid Chlorine
Hello all,
Been a long time reader and finally created an account today because I can't get a handle on what this stuff is.

I had an algae problem a little over a month ago. After a week of SLAMming, brushing, backwashing, the water cleared up pretty quickly. CC was 0.2, OCLT was 0.4. Then a week later, I started seeing some yellowish/brownish stuff begin accumulating on the bottom. When I brushed, the stuff turned dusty and made the pool slightly cloudy. I added enough liquid chlorine and brought FC up to shock level and kept it there for a few days along with brushing and backwashing. I woke up each morning and there it was again. It wasn't limited to the shaded areas and seemed to accumulate anywhere, so I didn't think it was mustard algae, but on the off chance it was, I went ahead and raised FC to Yel/MstrdShock level per the Chlorine/CYA Chart. After maintaining that shock level for 3 days, and again brushing and backwashing, the pool was finally clear. At the end of that SLAM my test results were:

FC: 18
CC 0.0
PH: 7.2
CYA: 30
TA: 120
CH: 200
OCLT: 0.4

Waited about a week for the FC to get back down to target level. The water was as clear as the day we filled it up 3 years ago. The family has been enjoying it for about 2 weeks. Then, I woke up yesterday morning to go test and the yellowish/brown stuff was back. Just one or two spots. Today, there was a lot more.

I've read through the forums and tried to educate myself as best as I can, but I can't figure out what's going on. I test every day. Target levels have been maintained. Pump has been running 24/7 since this all started. I'm not losing more than 0.8 ppm of FC during the OCLT. I've read that yellow/mustard algae is pretty rare, and is often mistaken for pollen. I didn't think it was pollen, because I haven't seen any floating on the surface.

These are results from today. (Taylor K-2006 test kit) CYA is a little higher because I added some stabilizer after the last SLAM when I thought the problem was resolved.

FC: 5.8
CC 0.2
PH: 7.4
CYA: 50
TA: 140
CH: 180
OCLT: 0.6 (Did a test last night)

Any help is appreciated!
 

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Welcome to the forums! Looks like you are already well versed in a lot of what is going on around here and have a K-2006 test kit! Kudos! I know how frustrating it is to finally get something clean, then poof (literally), something odd. But don't worry, that's why TFP is here! :)

I'm still new to providing assistance myself, so I am sure the others will chime in very soon with their expert opinions and guidance.

Just from my viewing, it sure looks like algae. Back when you had the algae problem, did it accumulate on the sides (not just the bottom)? Like brown/yellow stuff up the sides as well you could visibly see brushing it away. This is usually a way to distinguish between nature and algae. Nature being pollen, dirt and other not-so-harmful stuff. This time of year is rough for pollen. Which behaves very similar to some algae, not just mustard algae, except pollen won't be stuck to the sides of the pool.

Also, did you vacuum to waste the stuff from the bottom of the pool when you were vigilant at "clearing" it a few weeks ago?
 
Last edited:
Thank you for the feedback!

There were one or two spots where I could see it on the walls. But they were in areas that had full sun, so I wasn't quite sure what I was dealing with. Decided to play it safe and treat it as mustard algae just in case.

Yes, when I cleared everything a few weeks ago, I vacuumed to waste.

I also vacuumed to waste this morning and cleared out each spot I saw. That was 6 hours ago. I just went out to look again and I can already see little bits of it in the same areas. I thought for sure after slamming at mustard shock levels, I'd be home free.
 
I can't answer exactly why you have it but I believe you have algae. Probably not mustard algae but plain old algae.

There is one thing that triggers algae growth.......lack of chlorine.

I would suggest you increase chlorine levels to SLAM value and run the pump 24/7 and brush daily until it clears.

You have a good grasp of the concepts so just be diligent and keep your FC at SLAM value until it stops reappearing.

Vacuuming to waste is really not very productive.....better to brush up the "junk" into the pool water so the filter can grab it and do it's job.
 
CharlyT said:
Thank you for the feedback!

There were one or two spots where I could see it on the walls. But they were in areas that had full sun, so I wasn't quite sure what I was dealing with. Decided to play it safe and treat it as mustard algae just in case.

Yes, when I cleared everything a few weeks ago, I vacuumed to waste.

I also vacuumed to waste this morning and cleared out each spot I saw. That was 6 hours ago. I just went out to look again and I can already see little bits of it in the same areas. I thought for sure after slamming at mustard shock levels, I'd be home free.
Click to expand...
Have you changed the sand in your filter recently
I hand a similar situation with my pool . Tried everything nothing seem to work. Change out the sand, clean the filter unit and put it back together and Shazam. It solved my problem.
 
This is a suggestion I haven't come across yet. My understanding is that sand lasts 5, 10, 20 years or more, and doesn't degrade over time.
I did do a deep clean of the sand last November, since it was the 2nd year in operation, but the amount of particulates that came out was pretty small.
My pump pressure is in the green and the sight glass is crystal clear.

What's the reasoning behind changing the sand?
I would think there isn't algae hiding in the sand. With the FC at shock levels, I would think any algae lurking in the sand filter would get destroyed and ejected during backwashes.
 
Sand lasts forever and doesn't need changing - unless you've added floc or other needless pool store potions.
A deep clean every yaar or two should suffice.

Most likely your chlorine dipped below minimum.
What FC level were you targeting?
If the daily chlorine usage exceeds the difference between target and minimum, you can easily get a nascent algae bloom. This may have happened due to the increase pool usage recently.
 

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That was my understanding also.

After I completed the last SLAM, my CYA was 50, so I kept my FC between 6.0 and 7.0.
Today it dropped below 6.0 for the first time since the last SLAM to 5.8, but I assume that's because of the algae.
 
I always shoot for the high end of the range. Gives me more wiggle room.
And if bather load increases, I bump the FC upa little BEFORE the load increases and then again after.
 
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TFP teaches that sand needs a thorough Deep Cleaning every couple of years but NEVER needs changing.

During the Deep Cleaning, check the level of your sand to insure you have enough.
 
CharlyT said:
I had an algae problem a little over a month ago. After a week of SLAMming, brushing, backwashing, the water cleared up pretty quickly. CC was 0.2, OCLT was 0.4. Then a week later, I started seeing some yellowish/brownish stuff begin accumulating on the bottom. When I brushed, the stuff turned dusty and made the pool slightly cloudy. I added enough liquid chlorine and brought FC up to shock level and kept it there for a few days along with brushing and backwashing. I woke up each morning and there it was again. It wasn't limited to the shaded areas and seemed to accumulate anywhere, so I didn't think it was mustard algae, but on the off chance it was, I went ahead and raised FC to Yel/MstrdShock level per the Chlorine/CYA Chart. After maintaining that shock level for 3 days, and again brushing and backwashing, the pool was finally clear
Click to expand...
Just to clarify - the mustard algae slam levels are an additional step after a SLAM is completed successful. Because you were still seeing algae, you didn’t actually complete the first SLAM before continuing on.

My guess as to what happened is you were not done with SLAM the first time around, and the additional higher levels of mustard algae step caused the algae to get knocked back pretty well. But it wasn’t gone, so it returned. Typical advice would be to really inspect: steps, ladders, lights, weir doors, etc. You probably have an area with poor circulation and a healthy colony of algae.

For FC testing, just use 10ml sample size, each drop is 0.5. You don’t need to waste the reagents to get 0.2 resolution.
 
reggiehammond said:
Just to clarify - the mustard algae slam levels are an additional step after a SLAM is completed successful.
Click to expand...
Per the SLAM documentation, completion of SLAM is determined by the following:
  • CC is 0.5 or lower
  • AND you pass an shows a loss of 1.0 ppm or less)
  • AND pool water is crystal clear with no visible sign of algae (dead or alive) on floor and walls
I followed this process meticulously and met all the criteria for completion, CC was 0.0, OCLT was 0.4 and water was crystal clear, that would indicate SLAM is done. How would I know that I needed to raise FC to mustard algae SLAM levels?

This is the first I heard of this "additional step" and I haven't seen it in any documentation. But maybe I missed something.

Can anyone else confirm this? Seems a bit contradictory. If I completed SLAM, why would I raise my FC levels even higher if the documentation suggests the issue is resolved?
 
It is not likely mustard algae.

It is likely that you let your FC get low at some point after slam and it returned.
or
You pool wasn't actually clear...(when you brushed after passing oclt, did ANYTHING poof, show up?)

Having said that, here is the "extra step"...

www.troublefreepool.com

Mustard Algae

Today We are going to show you how you can get rid of mustard algae in your pool. By following the steps in this guide and with no expensive chemicals.
www.troublefreepool.com www.troublefreepool.com
 
PoolStored said:
You pool wasn't actually clear...(when you brushed after passing oclt, did ANYTHING poof, show up?)
Click to expand...
No it did not.

As I said in the original post, after the original SLAM, the water was as clear as it's ever been. So when you say the "pool wasn't actually clear" , I assume you mean, even though the water looked clear, the algae was still lurking, waiting for FC levels to drop so it could come back.

Thank you for sharing that link. I haven't seen that one before. This explanation makes more sense.
 
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CharlyT said:
As I said in the original post, after the original SLAM, the water was as clear as it's ever been. So when you say the "pool wasn't actually clear" , I assume you mean, even though the water looked clear, the algae was still lurking, waiting for FC levels to drop so it could come back.
Click to expand...
I mean that some members are not diligent with brushing during SLAM. They get to the point the pool is "clear," but if you actually brushed the walls, you could see poofing of algae coming off when they brush...this is not "clear." I have no idea if this is your case or not, just a possibility.
 

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