Brown staining on white fiberglass spa

[Matt]

I have a brownish stain around the entire top of a white fiberglass spa. It's about a half inch in height and goes all around the spa at the water level. They have no noticeable thickness and are translucent. They cannot be felt at all if you run your fingers over them.

The spa is bromine based. Current tests show:
Bromine: 5.4 ppm
TA: 140 ppm
pH: 7.4

I started the spa with brom start (NaBr) and every day have been adding bleach to bring bromine levels up to about 6 (then they decline overnight and during the next day). After adding the bleach, I test pH and add muriatic acid to balance to 7.4-7.6.

What is the likely cause of the brown stains? My guess is some kind of metal, but I'm not sure. I have a bottle of spaguard stain and scale control... would this be useful? It doesn't say what it is... is it a metal sequestrant?

Thanks.

Matt

 

[Guest]

Could be iron. Try holding a vitamin c tablet on one of the stained areas for about 30 seconds. If it leaves a clean area it's an iron stain and is easy to remove. Is your spa fiberglass or acrylic? If it's fiberglass then get your CH up to about 200 ppm if it's lower. This can help prevent staining. What pH do you maintain the spa at? How high does the pH get? pH spikes are what can lead to staining.
I would run the TA closer to 100 ppm. You will be less likely to get pH spikes that way.
If the stain is iron the best way to get rid of them is to drain the spa, fill with plain water, use ascorbic acid to remove the staining, drain again (to get rid of the iron in the water from the ascorbic acid treatment) and refill and rebalance. Add sequesterant to help prevent future staining.

 

[Matt]

I just drained and refilled it, and it happened. Any iron in there is iron from my tap water, so refilling won't lower the level. I'm pretty sure the spa is fiberglass but I'll verify that. I keep the pH between 7.4 and 7.6 generally. I add bleach to increase bromine levels which can spike the pH up to 8.0 or a bit higher (can't really tell on the test, but based on acid demand, it's not much higher), but it's only that way for 10 minutes before I bring the pH back down with acid. I'll try to buy a vitamin C tablet soon.

The staining actually comes off pretty easily with a soft bristled brush and a few minutes of scrubbing, but then comes back.

What do you think of that Stain and Scale Remover bottle I happen to already have? Would that help? I wish it gave ingredients... I can only guess as to what it is... I'm thinking it's a chelation agent / sequestrant, but for all I know, it could be apple juice.

How does Ca hardness prevent staining?

Do you know of any kits that test quantitatively for common metals that are reasonably priced?

I haven't added anything to the pool that would have iron in it (bleach, sodium bromide, baking soda, soda ash, muriatic acid, KMPS).

 

[Guest]

The staining actually comes off pretty easily with a soft bristled brush and a few minutes of scrubbing, but then comes back.

then it's not iron but probably a scum line from bather load. Try putting a scumball, scum bug, or sun sorb into your spa to collect body oils and if that doesn't work try adding an enzyme product weekly.

 

[Matt]

It can't be bather load either, it happened before the spa got used...

Is iron usually very hard to remove?

Basically, the spa had a ridiculous sanitizer demand (it was eating 10ppm bromine per day) because the person who was supposed to maintain it let sanitizer levels drop to 0 when I was away. Anyways, I drained the whole thing, then refilled, shocked with a lot of bleach for a day, drained that completely, refilled again. Then I balanced TA, then pH, then added NaBr and shocked with a pH neutral KMPS shock. This took bromine levels up to about 12 ppm (supposed to be 10, but the spa is a bit under 400 gallons and the tap water has some chlorine which might have oxidized the bromine).

Anyways, I noticed the brown staining first when I had the bleach in there, and then again after that was emptied and the spa was refilled. Each time I was able to remove it with the plastic soft bristled brush without too much effort. It's kind of a brownish-yellow (almost bromine colored, but I don't think it's bromine, just trying to describe the color).

My CH is probably too low, but I'm afraid to muck with it too much because I still cannot get a reliable endpoint on the Taylor test, even using 6 drops EDTA first. I still get tons of precipitate. It makes me wonder if we have a lot of metals in our tap water and some kind of chelation agent is necessary. We have no staining in the pool, but that was filled by the pool company. Over time though, a lot of tap water has replaced that original water.