Help please -- black algae or stains of some sort?

[TwinsPool]

I am in the midst of a SLAM procedure for a ~2-yr swamp, but now that all the heavy muck is gone and I can see the main drain easily (still cloudy though), I see dark mottled stains on the bottom and what looks like accumulation of stain at the rounded areas at the bottom of all the walls. Looks like my entire pool floor has the measles. Probably some on the walls too, but the floor seems to get most of it.

I thought it might be black algae, but I can't seem to scrape any sort of sample off with my thumbnail. It feels hard and rough just like all areas of the pool surface. I used a hybrid nylon/stainless steel pool brush on it (many hard strokes), but it does exactly nothing to these stains (maybe because I have already brushed with a 100% nylon pool brush??). I admit, though, that the nylon/stainless brush bristles are mostly nylon.

Then I thought it could be a metal stain of some sort, so on a step (about 1 foot deep), I poured a few ounces of highly concentrated muriatic acid, which I could see drop to the step and cover a patch of it (I did this twice in succession), but that did nothing to the dark stains. I even tried brushing the area after the acid treatment -- no change.

This picture is of a corner in the shallow end with my nylon/stainless pool brush for scale (it was getting dark so I used a flashlight):


And this is the step I mentioned above:

The light-colored strip on the right is the rounded area where this step meets the wall of the step above it. So there is much less of this stain on walls compared to floor areas. That effect is also noticable on the corner picture above.

One last possible clue. This step is the second step. The first step dried out recently this summer and has much much less of this stain. The first step looks a lot like the light-colored strip in the picture. However, I don't know if the first step looks better because it dried out or it was always like that. Just thought I should mention this difference though.

Any idea what I am dealing with, or what further tests I can do to find out?

Thanks!

 

[ajw22]

How do you chlorinate your pool?

Sounds like copper stains.

Get …

Stain ID Kit | Jacks Magic

jacksmagic.com

 

[TwinsPool]

I use liquid chlorine only. I haven't used any store-bought chemicals except chlorine and muriatic acid. I do have 1-1/2" copper pool plumbing underground of this 1977 pool. We bought the house 3 yrs ago (Sept 2021) and moved in only 13 months ago. A pool guy was maintaining the pool for the previous owner and we used him for a few months after buying.

The pool guy told me he replastered the pool but didn't say when. I think the pool was painted a dark green color during the replastering or the plaster was that color, because when I look at historical Google Earth pictures of the pool I see that the color changed in 2018. Maybe the "stains" I see are degraded paint??? But, if so, why would "staining" be darker on the bottom vs the walls? Here are the historical Google Earth pictures, FYI. Upper picture is my pool (irregular hexagon) and lower pic is a neighbor's pool (kidney shape):



Regarding Jack's Magic: It's instructions say to have the pool balanced before using it, and two of my measurements are outside their prescribed ranges. I'm SLAMming, so my FC is in the mid-teens, and my TA is 150-180. They want FC at 1-3 and TA at 80 or below. They also ask for Total Dissolved Solids, which I don"t know how to obtain. Would Jack's Magic still work?

 

[ajw22]

Get your SLAM done before you try and deal with stains.

One problem at a time.

Once the SLAM is done let's revisit your levels.

 

[TinFoilHat]

If the pool was painted and since the experts say paint in a pool only lasts a couple of years before it has to be repainted it sounds like you're on the right track. The lighter color on the upper benches will be more sun faded than the paint deeper in the pool.

 

[TwinsPool]

Paint remnants fits some, but not all, of the symptoms. I would like it to be something simple like fading/failing paint, but, if it is paint or even a stain, why would the walls have no, or little, of it left, and why would it look spotty (like colonies of something growing), and why would it accumulate at the bottom of walls? I would just like to be sure it is not something like black algae that may need to be removed before swimming. I presume we can swim with a paint or stain problem. (I'm getting heat from the family about having no pool this summer.) I've heard/read that rubbing it with a chlorine tablet/puck can determine if it is black algae (if it is lightened significantly when rubbed/scrubbed with the puck). Anyone here have info on that? I'll ask a neighbor if I can borrow one of their pucks.

 

[TwinsPool]

ajw22, I finished the SLAM (crystal clear water, etc) and am now trying to get the pool balanced and work on these terrible stains, which are worse than I thought now that I have crystal clear water that shows everything on the bottom.

My recent numbers FYI:
FC 9
CC 0.5 (sometimes is 0.0 but never more than 0.5)
CH 200
TA 160
CYA 30
pH 7.5 (I've been adding 31% muriatic acid (a quart a day) for a couple of days, but it has done nothing to the pH (or the TA). I'm still adding to see if I can lower the pH in an attempt to get the TA down.)

I bought the Jack's Magic Stain Identification Kit, although I'm actually pretty sure the stains are copper, as you first suggested above in post #2. I will post a picture tomorrow of the bottom stains. The Jack's kit wants the FC to be 1-3 ppm, which would seem to invite algae with my CYA of 30, so I'm a little concerned about that.

Another thought... In looking at the color of the pool now, it seems to be a VERY similar color as the oxidized copper undergound pool pipes I see next to the pool equipment. This makes me now think that the color change of the pool in 2018 (see pics in my post #3 above) is not due to plaster color or painting but is due to staining from the introduction of a lot of copper into the pool water, perhaps by an algaecide or chlorine pucks and/or other additives. It may also be possible that the water has not been changed since then either so the copper may still be present.

One thing that makes me think copper is still present is that a few days ago I put a trichlor puck on a pool step to see if it would bleach the stain (thinking it might be an organic stain), but what I got was mainly a precipitation of more staining surrounding the puck. If I am not mistaken, either the chlorine or the CYA acidity is oxidizing metal in the water and causing the stain. Do you think the stain is a copper precipitate coming from the water?

Here are some pictures of the puck experiment (I removed the puck already). I moved the puck from one position to another. For the lightest effect (lowest puck position in the picture) had the puck there for about 2 hours, and the puck was present for progressively longer periods as the circular stains were more intense (one day, then several days). If I/we are right about the stains being copper, I'm wondering if I will have to resort to the Zero Alkalinity Acid Treatment (The Zero Alkalinity Acid Treatment). Is there another way?

 

[TwinsPool]

If people are still out there, here is a picture of the stains on the pool bottom, from the shallow-end steps (upper left of pic) to the deep-end main drain (right side).
Picture was taken at night with the pool light and an outside flood light on.
You can see the shadows of the diving board and a vacuum hose in the deep end.
The prominent left-to-right streaks of dark stains are located at the bottom of the pool's side walls. Pool deck is seen at the top.
The stains are pretty horrible -- they cannot be brushed off.
I need advice on options on removing the stains. Although not proven, both the very dark parts and the general blue-green color of the plaster may be stained with copper.

 

[ajw22]

Looks like copper stains.

Confirm using Stain ID Kit | Jacks Magic

Don't leave a trichlor puck sitting on your plaster so long as it will permanently etch a ring on your plaster.

Removing copper stains requires sulfamic acid and then draining the pool and refilling with copper free water...

Copper in Pool Water - Further Reading

www.troublefreepool.com

 

[TwinsPool]

Thanks for the link to that article in the wiki. I had not seen that one.

As I see it now, there appear to be about 4 ways to get rid of these presumably copper stains:
1. Sulfamic acid, then drain the pool (not draining becomes a many-month nightmare according to some)
2. Muriatic acid, then drain the pool (Zero Alkalinity Acid Treatment)
3. Drain the pool, then muriatic acid wash/scrub surfaces
4. Drain the pool, then power-grind off stains with diamond grinder or power-sand off with diamond paper (I know someone who did the sanding by hand, but the stains were probably less than mine).

My next door neighbor has drained his pool for replastering and feature additions, so I presume I can drain my pool safely without it popping out of the ground (this is SoCal, afterall -- basically a desert).

All of the options have their drawbacks, but I am slightly leaning toward #3, since 1) it seems almost guaranteed to work on serious stains, 2) is quick (maybe about 2 days or so), 3) I could hire someone to do it, which is both a pro [easy] and a con [a little expensive].

For now, since we have two pool parties planned in the next week, I will put this decision off for a while.

If anyone has strong positive (or negative) preference for any method based on experience or knowledge, I would love to hear about it.