Yellow Spots on Pool Wall

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PoolFrog

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Aug 9, 2013
130
Dallas, TX
Hello,

A few days ago, I started noticing yellow spots/stains on the wall of our deep end. I tried brushing over the weekend, but this didn't seem to have any effect (no dust clouds or anything). The water is checked & chlorinated every day with bleach, and remains crystal clear. The only chemicals that we've added to the pool since buying our house in June are 8.25% bleach and 20 baume muriatic acid periodically to lower the pH (creeps up frequently).

Below are my numbers from today's tests (TF100):

FC - 7 (just added bleach to bring up to 9, where I prefer it to be)
CC - 0.5 (bringing FC up to 9 usually 0's this out)
TA - 100
CH - 860 (haven't checked this in weeks. It's high because previous owner used cal hypo weekly)
CYA - 50
pH - 7.4

Any thoughts on what these yellow spots could be?

Thanks!
 

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Have you ever had your water tested for metals? Do you fill from a well? One of the few things you could at least start with by getting them tested at the dreaded pool store. Otherwise there are test kits for metals as well as contacting a local laboratory to test accurately either the pool water or fill water. Holding some vitamin C tablets on the stain for a few minutes might fade/eliminate a metals based stain.

You could also try holding a trichlor tab on the stain for a few minutes to see if that fades the stain, indicating one that's organic (algae) in nature.

I would also try an overnight chlorine loss test (OCLT) to see if there is anything growing in the pool. Bump the FC to 10-12 when doing an OCLT to get a better idea if there is something lurking.
 
We've never had the water tested for metals, but I'm open to having the pool store check it for me. If that's the case, is there a product that is recommended that I should buy from them? Our water is municipal, so not well water.

I can also try the OCLT after I bump up the FC a bit more.

Thanks for the suggestions!
 
If you do have your water tested for metal, make sure you grab a sample from the hose spigot not the pool. No sense trying to test water once chlorine has been added. If you do have metal (iron or copper), let us know and we can give you a list of recommended products that have worked well here. If there are no metals, or enough to really register and have an impact, then we'll reassess and go from there.
 
I haven't had a chance to go to the pool store to have the fill water tested for metals, but I did do the OCLT last night. I raised FC to 12 yesterday afternoon.

Evening after sundown:
FC - 12
CC - 0.5

Dawn this morning:
FC - 11
CC - 0

I also swept the spots again yesterday afternoon, and did see some disappearance, but still no clouding. If these spots are due to metals in the water, would I still only see them in certain areas of the pool rather than all over?
 
They (metal stains) could present themselves just about anywhere around the pool - floor or steps mostly I would assume. But the fact that some of them did disappear would indicate they are not stains from metal. Metal stains take a bit of chemical treatment and/or elbow grease, so that may be a good sign. Also good you passed an OCLT this morning. Say, are those yellow spots in your deep end in shaded areas by any chance? I'm wondering if we don't need to consider Pool School - Mustard Algae. Just a thought.
 
Yes, they are only in a particular spot of the deep end that is directly underneath a large tree and sees very little sunlight. I was concerned about the possibility of mustard algae for that reason, but wouldn't' I have seen a drop on FC this morning?

I forgot to mention that the pump wasn't running during either FC test (had already shut off for the night before the evening test, wasn't yet on for the day for the morning test).

We also had a high pH prior to noticing the yellow spots, for what it's worth. It had climbed to 7.9 or so before we were able to add acid enough to lower it. It's now at 7.5.
 
Does seem odd huh. You would think there should be some drop in FC, regardless of the algae type. Well, your call, but since just successfully completed an OCLT, before the weekend gets here you could (if you wanted to) raise your FC to MA level per the Poolmath calculator to see if that remedies the yellow areas. MA level FC is for 24 hours, but then you could let it sink for the weekend. Something to consider anyways. Maybe some other suggestions will post to this thread as well. Keep us posted!
 
Using PoolMath, my normal FC range is 4 to 8. As I mentioned earlier, I prefer to keep it at 9 (I have a small child who is probably urinating occasionally in the water - gross, but this is just how I deal with it). PoolMath says my MA level for FC is 25. Our calcium was 860 last time I checked. Should I be concerned about possible damage to our pool equipment at a FC level that high?
 
Using your current CYA of 50 and a 20K pool, I entered everything from post #1 into the calculator and it gave me a Mustard Algae FC level of 29. Your CSI range is within normal levels, so I don't see any problems with continuing. Your plaster is not new is it? If not, you should be fine at MA levels for 24 hours. No swimming during the MA treatment though. After that, keeping your FC slightly higher than your normal target of 6 is fine.
 

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Sorry, I need to update my sig. We've figured out that the pool is closer to 23,000 gallons, so that's the number I've been using on Pool Math for the last several weeks. However, I understand your point about safety to the pool equipment at these FC levels.
 
Texas Splash said:
Does seem odd huh. You would think there should be some drop in FC, regardless of the algae type. Well, your call, but since just successfully completed an OCLT, before the weekend gets here you could (if you wanted to) raise your FC to MA level per the Poolmath calculator to see if that remedies the yellow areas. MA level FC is for 24 hours, but then you could let it sink for the weekend. Something to consider anyways. Maybe some other suggestions will post to this thread as well. Keep us posted!
Click to expand...

Not sure if you caught it or not, but in the previous post they mention they didn't have the pump running for the OCLT.

It might be a good idea to run it again tonight.

Make sure you test, pump running, close to dark, and again before the sun is a factor.
 
PF, just to be clear ..... you certainly can run an OCLT tonight/tomorrow if you wish. But if/when you bump your FC to the higher mustard algae level for 24 hours, there's no OLCT for that one. It's assumed you already passed from the regular SLAM. But keep this in mind from the MA page:
While at mustard algae shock level you need to thoroughly brush the entire pool, including walls, floor, steps, skimmer, under ladders, everywhere. All pool tools and toys and anything else that is used in the pool needs to be wiped down with a dilute bleach solution or soaked in the pool for an hour while at mustard algae shock level. Bathing suits should be run through the laundry. If you have underwater lights, they should be removed from their niche and the niche brushed out, and then the lights replaced. If you have fountains, or waterfalls, or other water features, they need to be run for at least an hour while at mustard algae shock level. Be very thorough, or you will most likely just need to do it all over again.
Click to expand...
Good luck!
 
Finally got to redo the OCLT with the pump running for both tests, and I actually saw no loss of FC. My CC is between 0.5 and 1.0 (solution didn't look 100% clear after the first drop, so I added another). Is it still safe to say that the yellow on the walls could be mustard algae? It is brushing away in some places.
 
Ok, will go stock up on bleach. I've never dealt with FC levels anywhere near what I'll have for MA level. I know we already talked about safety to pool equipment, but I forgot to ask about our Polaris 280. It's in the water at all times. Should it remain in the water for the MA shock, or should it be removed for its safety and/or that of the fabric bag?
 
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