What's causing this stain in my new hot tub?

Esand323

Well-known member
Aug 6, 2018
94
Indianapolis
Hi all,
I recently purchased a hot tub. After a couple months of frequent use, I noticed this brown stain down by the return. I'm not sure the technical term, but it's the water return jet that is running constantly and has hot water. What is this brown stain from? Do I have too many metals in my water? Could it be from high iron? I did fill my hot tub up from well water (don't really have a choice). However, I used a hose filter and put in an entire bottle of Metal Gon in it.

Anything I should do? I'm planning to do a refill here this week, so I can probably clean it pretty well then. If it is related to high levels of metal, what should be done? My TF-100 doesn't test for metals. Should I invest in a kit that will?

20201117_154547.jpg

This picture doesn't really show the stain all that well. It's much more pronounced in person, but you can see some of the brown in the picture.

Thanks!
 

Esand323

Well-known member
Aug 6, 2018
94
Indianapolis
Thanks for the help. I test chlorine/pH everyday and TA, CH, CYA every week. I wasn't able to test last week so a couple things got off.

  • Chlorine: 6 ppm
  • pH: 7
  • TA: 70
  • CH: 275
  • CYA: 70

My TA got too low which threw off my pH. I used the pool calculator and added the appropriate amount of baking soda and my pH is now reading 7.4. CYA also got a bit out of hand as I switched off dichlor too late. I had a neighbor add dichlor every two days while I was gone last week.

I noticed this stain about a month ago when everything was much more balanced. I was able to wipe away most of it with just my hand.

I'm doing a water change this weekend anyways, but I did fix the pH for the time being. I'm testing using my TF-100. I know I don't have a smartchlor or salt generator. I believe it does have ozone has on my order form it says "Ozone: CD Ozone". It says it also has a propure chamber.
 

RDspaguy

In The Industry
Mar 21, 2020
1,210
Cabool, Mo
a month ago when everything was much more balanced.
???
I'm really not sure, chemistry is not my specialty. I'm sure @JoyfulNoise will respond tomorrow, I am just gathering the info he's going to need.
What were your readings when you first noticed staining?
How much metal gone does the manufacturer recommend?
What brand of spa?
 

Esand323

Well-known member
Aug 6, 2018
94
Indianapolis
The readings have always been good until this past week. I don't have a log of the exact readings, but I was checking frequently and had no issues. The manufacturer makes no mention of the metals. The dealer used the "Leisure Time" product line for start up chemicals when I bought it. This included their product "Metal Gon." It states to use a full 8 oz bottle for up to 500 gallons. The entire bottle was used at start up. Being just a sequestering product, I wonder if it wore away?

I have an Oahu Elite Tropic Seas Hot tub by Artesian. 475 gallon.
 

CuckooChris

Well-known member
Sep 14, 2016
61
Coplay, PA
No expert here, just learning, but do you have a pleated filter? Does it look orange? The stain looks like a metal stain and from my experience the filter would be stained also (if it was from the well water). But if that's the only place in the tub with the stain, then it's kind of strange.
 

Esand323

Well-known member
Aug 6, 2018
94
Indianapolis
Thanks for the reply. Yes, it's a pleated filter. I don't recall it looking very orange. I'll take a look tomorrow when the sun is back out. Yes, it's only this one place. I have a circulation filter that runs 24/7. So I figured the constant pressure from the jet there is what is causing the stain.
 

RDspaguy

In The Industry
Mar 21, 2020
1,210
Cabool, Mo
Well, ozone is a powerful oxidizer, which theoretically could cause metals to come out of solution. This would explain the location. I personally have never had this issue, but I don't have alot of metals in my water and don't even use metal gone.
It is also likely inline with the heater, which could be a factor if your chemistry is bad. No disrespect, many people do an excellent job maintaining their water, but everyone says they do an excellent job of it. ;)
It could also be something dropped in a pipe during manufacturing. I have seen it before.
 

Esand323

Well-known member
Aug 6, 2018
94
Indianapolis
Thanks for the help. Much appreciated. How would you suggest cleaning it. The manufacturer says 1 part vinegar to two parts warm water when cleaning the shell. I'm not sure that would remove the stain though.
 

RDspaguy

In The Industry
Mar 21, 2020
1,210
Cabool, Mo
Vitamin c tablets. Use them like an eraser. You do not have to drain to do so. If it's already drained, you can use muriatic acid and water. Just don't get any on the metal jet escutcheons.
 

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DangerBoy

Well-known member
Oct 4, 2018
153
Calgary/Alberta
@Esand323, the stain appears to be an iron stain which you would get even at a low dissolved Fe concentration. Here in Canada, the various water quality guidelines that are in use all set the guideline limit for dissolved iron at 0.3 mg/L or ppm. I suspect the US guideline limits are similar. This limit is based on aesthetic objectives; any more Fe than this can give the water a bad taste and can leave iron stains on plumbing fixtures, etc. If the water you're using has a bit of Fe in it, that would explain the source of the Fe causing the staining. It wouldn't be uncommon for groundwater to contain slightly elevated Fe concentrations causing this sort of problem. A proper iron filtering system may be what's required to eliminate the problem.

One thing you might try is maintaining your system at a pH of 7.5 or 7.6 instead of 7.0. In other words, slightly basic/alkaline instead of dead neutral pH. That will give you a little bit of a buffer zone between your system pH and going slightly acidic. At 7.0, it doesn't take much of a swing to make your pH go slightly acidic. From what I know, it's always best to stay just slightly on the basic side of neutral but not too much. Setting your system pH at 7.5 or 7.6 would be just about perfect.
 
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