brown spots

[drwill]

So I had the plaster (diamond brite) redone a few months back as part of the pool remodel and now I'm finding a few light brown patches here and there. There are a couple on the steps of the pool and a few in the deep end. They absolutely do not brush away with vigorous brushing from the diamond brite metal/nylon brush. I also tried rubbing one of the spots on the steps with a chlorine puck last night and it did not seem to have any effect. Then I tried rubbing the spot with a vitamin c tab (thinking it was iron) and that also had no effect whatsoever.

Prior to having the diamond brite done, the pool had a few of these exact sorts of spots already which is what makes me think it is a chemical and not an algae. The pool has always been crystal clear since we bought the house almost a year ago. I've never had even the slightest green tint to the water. I added borax to the pool last night and, against my better judgement, I've got some polyquat 60 to add to the pool tomorrow in the event that this is some sort of algae growing which I think is unlikely. Chlorine is at 4 ppm currently but I often let it get low without ill effect. Ph always climbs, probably b/c of the new plaster and a small suction side air leak that I think I've finally fixed... but i try to stay on top of it and don't let it get crazy or anything like that (maybe up to 8 or so). CH, according to the pool store (I have a basic test kit), is at 380. CYA is at 30ppm.

So if the vit C tabs and chlorine pucks don't seem to do anything, what could it be? It's light brown in color and the spots are maybe the size of a penny and about that color. I don't think it's "rebar pop" and there are no other metal objects in the pool. I filled the pool with municipal water in South FL which does not seem to be high in iron - no rust stains in my toilets or on my house from the sprinklers. Thoughts?

 

[pwrstrk]

I'm not totally sure what the spots are, but I am sure that letting your FC fall below the min level for your CYA level is not a good practice. You should never let your FC fall below 2 if that is an accurate CYA level. How are you chlorinating your pool ? The same goes for your PH. You should not let it get above 7.8 and be lowering it with acid. The addition of Borax will raise your PH. The polyquat will not kill algae. It is only an algae inhibitor.
I'm going to suggest that you look into getting yourself one of these test kits. It sounds like you've been using the pool store for some of your water testing. For the most part their accuracy is not up to par. A good test kit will go along way in helping you maintain your pool. When you get a good test kit post up a full set of results for us to have a look at. It will help to determine what your spots are.
http://www.troublefreepool.com/content/124-pool-test-kits-comparison
Make sure you do some reading in pool school. These are some good articles to start with.
http://www.troublefreepool.com/content/123-abc-of-pool-water-chemistry
http://www.troublefreepool.com/content/142-how-to-chlorinate-your-pool.
Somebody else should be along to give you more insight on your spots. If you could add all your pool and equipment info to your sig it will help us help you better. ?

 

[JasonLion]

Try letting a vitamin C tablet sit directly on a spot until it dissolves and see if that does anything.

Photos might help us figure this out.

 

[drwill]

To be clear, I am very good about the chemicals. My wife thinks I'm fanatical and she may be right. I might be as diligent as some others on this forum though. I really don't let the pool go for more than a few days, never more than a week, without adding bleach or acid and testing. The pool gets brushed with the diamond brite brush a couple times a month and I vacuum it manually if there's anything on the bottom. I mean it when I say the pool really has never been anything other than crystal clear.

I think I get away with the low FC on occasion because the pool is coolish - partly shaded and screened. This also means we don't use it much (low bather load). But all that is about to change because we just had solar installed (woohoo).

The polyquat was a stupid splurge at the pool store the other day but since I bought it I'm going to add it and we'll see if it changes anything but I'm not holding my breath. As to how I added the borax, I added it along with the muriatic acid in two steps exactly as outlined on these forums and the PH came out perfect. I ordinarily use muriatic acid to control the PH which tends to climb - the pool store is always pushing sulfuric but I believe I read somewhere that that can be bad for plaster if you're using a lot of it.

FC is at 5 ppm, CC at 0, CYA at 30. The are currently 2 pucks in the floater, I want the CYA at 40-50.
Ph is 7.6
TA 75 (low I know, I'm going to add 3-4 lbs baking soda today - I usually keep it around 100)
CH at 380

- - - Updated - - -

edit: I tried rubbing/grating a vit C tablet on the spot for a minute or two but that didn't seem to do anything. I'll try letting one sit and will post back with pictures.

 

[drwill]

Ok, I tried letting the tablet sit for a good while (washed 2 dogs in the meantime) and to my surprise the spot pretty much went away. It sort of spread out and faded to the point where you probably wouldn't know it was there if you didn't know to look. So maybe it is iron. Assuming it is some sort of metal staining, what do I do? What sequestrant is recommended and is there any chance that it could react with a sequestrant that the pool remodeler might have added last Fall? Or react with the borax? Or Polyquat 60?

 

[duraleigh]

I would continue to apply pucks to the stains until they were minimized. Then, do nothing but observe, they may not return.

 

[whalers11]

Look up. Could the stains be coming from rust / rusty screws on your screen enclosure?

 

[drwill]

Screws from the enclosure is a good guess since the enclosure is old and does drop screws now and again but this is always around the doors (worked loose from us opening them), I've never found a screw in the pool and I manually vac it if there's ever anything there.

I think the issue is that I've let the PH drift upward too high. The pool is pretty acid hungry and this has probably as much to do with the new plaster as it does the suction side air leak. I did add some jack's "pink stuff" which I conveniently found on clearance at leslie's, I may go back and clear out the rest at $10 a bottle. I guess I have to add the phosphonic acid regularly for it to continue working, although perhaps if I am just more diligent with the PH then the sequestrant won't be needed. I'm not too keen about regularly dosing it with the pink stuff but, on the other hand, I don't want any more unsightly brown spots on my new plaster.

Edit: I read somewhere about putting the vitamin c tabs in a sock and holding that on the stain. Any idea if this is the best way to go about it? Some of these spots are in the deep end and against the wall. It's a spot where the vit c tab won't really sit on it's own but I may be able to hold a sock in that area with my foot. Should I do this with the chlorine at a low level? I read somewhere that the tabs work best when chlorine is low.

 

[chem geek]

The ascorbic acid (vitamin C) will react with chlorine so they counteract each other. That's why a full ascorbic acid treatment is done with the chlorine at zero or will become zero after adding the ascorbic acid. For testing a localized area, you shouldn't have to have the chlorine at zero if the tablet is in direct contact with the stain, but try and avoid circulation in the area to keep the chlorine from getting near the tablet. If the stain is iron, it should lighten from the ascorbic acid.

 

[onBalance]

The brown spots have nothing to do with high pH or chlorine or other water chemistry issues.
To me, the spots look like fertilizer granules that contain iron that fell into the pool. That type of iron stain is more stubborn to remove than typical rust spots.
Continue with your program, and they will eventually disappear.