Splotchy dark stain, looks charcoal at first observance

[BigIslandPoolService]

Aloha Friends!

I recently surveyed a 3-year old pool about 300 feet from the ocean...nice property...but the owners' beautiful turquoise plaster has developed a splotchy dark stain (looks charcoal at first observance). After receiving the first phone call in which she described dark spots, I expected to find dark algae spots (customer said she almost never shocks and rarely tests!). However, I found a pool with clear water and in surprisingly good balance (7.5 pH, 4.5 ppm FC, 0 ppm CC, 60 ppm Alk, 200 ppm CaHard, 40 CYA, Temp. 77). However, they have been using 3" tri-chlor tabs in the skimmer basket, and I'm beginning to think that perhaps the years of acidic & chlorinated water hitting the pump when the timer comes on may have slowly added metal(s) to the water until they finally noticed this stain (a couple of months ago).

I have no experience with this particular pool, so I'm trying my best to be a Sherlock Holmes and figure out what is causing this problem.

My first idea about the culprit was colloidal silver algaecide (due to the blackness of the stain), but the customer said they have never used any. Their water sources are: rain (60 inches per year at this location), roof catchment (Architect 50 composite shingles running into a concrete tank painted with epoxy), and truck-delivered County water (seldom due to cost). They have a rarely used waterfall that runs into the pool over natural stone, tile, and perhaps a little bit of "mock rock" dark-stained concrete (maybe iron used in that stain?).

I have no source to purchase Citric Acid until Monday...so I thought I would upload photos to see if any of you have any ideas...note the bottom drain...no precipitating due to high speed water flow around edges? And around the drain, I note that I actually see tinges of yellow and red at the edges of the black. But the other photos only show black, no other colors. Weird...

As usual, thanks to you all in advance...it is such a blessing to have the privilege of drawing upon your collective experience!!

Aloha!

 

[JamesW]

It's good that the chemicals are currently in balance. However, that does not mean that they have always been in balance. In fact, the chemistry seems suspiciously perfect for a pool where the homeowner claims that they rarely test the water. There's no way that a tab pool, that has not been tested on a regular basis, has those numbers.

I suspect that the chemistry has recently been corrected after being seriously neglected. I think that copper is the most likely cause of the staining. I doubt that the plaster was originally turquoise. I think that the turquoise color is most likely from copper.

If the plaster was originally turquoise, then it would be difficult to see most copper staining, because most staining is turquoise.

What is the service history on this pool?
Have the owners been doing all of the maintenance, or have they relied on a pool service?
If it was being serviced by a pool company, why is the service company no longer servicing this pool?
Are there maintenance records available? If not, why not?
Is there, or was there ever, a heater on this pool?
Is the current owner the original owner, if not, how long have they owned the pool?

 

[BigIslandPoolService]

Thanks James...but it really is a turquoise green/blue plaster...the owners designed and had the pool built for them, and have maintained it themselves from the start. And they live 300 feet from the ocean in Hawaii, so it is not heated (they DO use the 3" TriChlor with copper added though). The stain is the blackish/grayish stuff, but the light splotchy areas are what makes me scratch my head...they are on the walls too, so they weren't created by granules of acid or chlorine sitting there. They may just be parts of the plaster that have eluded the precipitation of metal staining--the normal unstained plaster--but why do THOSE PARTS resist the metal? Weird!

I'm now thinking it just looks dark because it is an iron stain, and the red/yellow components of the iron stain mix with blue/green light from the turquoise plaster to make a dark color--and that if the plaster were white, I would have instantly recognized it as iron staining.

The wife said they have rarely had problems with the pool. It got a session of algae at one time, but they were able to shock it out (probably Cal Hypo) and get things back to normal. I'm figuring that the raise in pH from that shocking may have led to the pool precipitating any metals that had been suspended until then. The wife says she just noticed this blackish stain two months ago, and that it had been a smooth turquoise color before that. I'm going to town to purchase some citric acid today, and I will do a careful test on the stain later this week. If it removes it, I plan to use citric acid, sequestrant, and CuLator to remove the metal from the water. It is a real tough protocol to follow here (no chlorine and warm temperature), as the marine algae blows in off the ocean, and there is always green algae growing around pool edges (I have to spray monthly with bleach/water), so I'm hoping the Polyquat 60 will do a good enough job. Trying to bring up the chlorine slowly in this territory is just asking for algae, so I hope the CuLator works quickly on this one.

 

[ROB N]

looks like it may be calcium scaling... are the splotchy areas abrasive and feel like sand paper?

 

[BigIslandPoolService]

Aloha Rob! Thanks for your help!

Nope, they are smooth as the plaster...and the customer's pool showed 200 ppm Ca Hardness...so I don't think it's calcium...