Not sure if Algae or just dirt

[hartpump]

Hi Pool Gurus, I am in year 3 of pool ownership. I have learned so much from this forum and I thank all of you for making me a more confident and knowledgable pool owner. I have learned how to maintain, open and close my pool from all of you generous individuals. Many thanks.
Last season when we closed, I noticed a light brown "dirt" on the sides of my in ground pool. The funny thing is that during the year my water was clear but at certain angles and at certain times of the day, it looked like the sides of the pool were dirty. My water was always very clear though, no haze or apparent algae problem. I use the TF 100 testing kits and my numbers were in range for the season. The pool is a plaster bottom with vinyl sides. No liner. I scrubbed during the season but it didn't seem to want to come off with a pool brush or vigorous scrubbing in pool with a handheld brush. So now as we head into pool opening time in Ohio, can you give me any suggestions as to:
A. Is this Algae or Dirt?
B. Whichever it is, if normal scrubbing with a pool brush wont take it off, what will?
I don't want to drain all the water out to scrub it obviously.
Any advice would be greatly appreciated.

 

[HermanTX]

If you an do an Overnight Chlorine Loss Test that will define if you have algae or not.

It could be staining.

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[Lake Placid]

The pool is a plaster bottom with vinyl sides. No liner.

This is an interesting construction. Are you sure the walls are vinyl and not fiberglass? What is the age and history of the pool that you’re aware of?

 

[hartpump]

This is an interesting construction. Are you sure the walls are vinyl and not fiberglass? What is the age and history of the pool that you’re aware of?

I could be wrong about vinyl. As I think about your question it is likely rolled fiberglass. So these PB's have been in business locally for over 50 years. They excavated the design, poured the bottom, the steps and the ledges. Then they used steel stakes along the perimeter of the concrete. They then used a roll of what i assumed was a heavy vinyl but more likely fiberglass. (I am dumb but I am slow). That material gave the upper wall shape to the pool. They then hung large long bags between each steel stake and filled them with concrete. After the concrete cured they backfilled everything. Lastly they covered the concrete in Plaster or gunnite or lord knows what. I should know i am sure.

 

[Lake Placid]

I could be wrong about vinyl. As I think about your question it is likely rolled fiberglass. So these PB's have been in business locally for over 50 years. They excavated the design, poured the bottom, the steps and the ledges. Then they used steel stakes along the perimeter of the concrete. They then used a roll of what i assumed was a heavy vinyl but more likely fiberglass. (I am dumb but I am slow). That material gave the upper wall shape to the pool. They then hung large long bags between each steel stake and filled them with concrete. After the concrete cured they backfilled everything. Lastly they covered the concrete in Plaster or gunnite or lord knows what. I should know i am sure.

Seems likely you’ve got a Hybrid construction pool. Concrete floor with Fiberglass walls. What is the age of the pool?

 

[hartpump]

Seems likely you’ve got a Hybrid construction pool. Concrete floor with Fiberglass walls. What is the age of the pool?

The Pool was built in September of 2020

 

[hartpump]

And in looking at the pics from the build they used Diamond Brite over all the concrete surfaces

 

[Lake Placid]

As mentioned by @HermanTX start with an OCLT to rule out organics.

The reason I was inquiring about the age and construction of your pool is that in older Hybrid pools, especially those with osmotic blistering, you will often find the issue you describe. I believe it’s generally a degradation of the gel coat where the surface becomes rougher and that can harbor dirt or the worn finish under the right illumination can look dingy, tired and old. It can manifest as a yellowish tint in the water, especially at dusk or night.

Given the relative newness of your pool I would not initially consider gel coat issues. So proceed with the OCLT and from there if it comes back good we can look towards stain diagnostics and the potential cause. Have you felt the walls with your hand when this problem manifests?

 

[Newdude]

In to learn more about this cool pool



Got any pics with it filled ?

Just today I noticed a yellow dusting on my car and I'm due east of you so we should be popping spring together. This time of year is tricky because the debris could be algae, pollen / farm dust, or both. We await the results of your OCLT.

 

[hartpump]

It's is still covered right now. I was trying to get a jump on the plan for when I remove the cover. It's still a little chilly here in Northeastern Ohio. I surely have photos from when it was open this past season.

 

[hartpump]

Update on stain issue. So I uncovered and looked at the stain some more. I drained enough water to get to the fiberglass sides where the discoloration is. I hit it with the pressure washer and it didn't touch it.. even with the Zero nozzle. I then thought well maybe its iron deposit because when dry it has a red hue to it. I had some CLR laying around and I brushed it in and it took it off. I will include some photos and let me know if you think it's iron in the well water. If it is, how do I prevent this if I have to top off with well water. I am going to have my water tested and am considering installing an iron filtration system.

 

[hartpump]

After I posted I started searching around for Iron staining issues. ( I know i did it backwards). So I see there are some things you can do to prevent iron staining.

 

[LaurenB]

For future reference, you can also use a vitamin C tablet (like a supplement), hold it on the stain and it will work like a Magic Eraser if it's iron. Guess it's too late now that you've drained

I also have very hard well water and ran into this problem. My solution was never top off with well water and use a solar cover diligently to avoid evaporation - and pray for rain!

 

[LaurenB]

P.s. I installed a filter on my hose and it still wasn't enough. I think you would need an actual water softening system.

 

[hartpump]

So the CLR didn't end up working on the stains. I ended up using Muriatic acid at 2 parts water to 1 part acid and scrubbing it by hand. That took care of most of it. I still have a weird "ring" around the bottom of the fiberglass about an inch off the bottom. I will include pictures. It feels like when you have residual adhesive on something. If I rub it hard enough with a finger it seems to come off, like glue. Thoughts ?

 

[hartpump]

P.s. I installed a filter on my hose and it still wasn't enough. I think you would need an actual water softening system.

I do have a softener system but in the past I have bypassed it when topping off the pool. I will stop that practice. I am also investigating a whole house iron filtration system. Since trucked in water is around 800 - 1000 dollars, I should be able to get a basic iron mitigation system for that price and go from there. I also understand I need to do more to sequester the iron that will still be in the water.

 

[hartpump]

I am still relatively new to maintaining a pool, This will be my fourth season. I feel like I have a decent handle on the chemistry. However, mistakes have been made. Short version of the story is I had iron stains on my fiberglass walls starting last season. I believe it's from topping off with well water. I closed up thinking I would address it this spring. I ended up draining the pool to power wash the sides. Ignorant me learned fast that that wasn't gonna work. Anyway, some Muriatic acid and lots of scrubbing later and it's pretty good. However I have something on the walls that even the acid wouldn't budge. I will attach pics. It feels almost gummy to the touch. A little like a glue residue. If I rub on it hard enough with my finger I can feel it start to move. Like when you are trying to get a label off a new drinking glass. The residue left after you feel the paper off. Thoughts on:
1. What is this?
2. How did it develop?
3. How do I get rid of it?

 

[hartpump]

Final update, I got whatever the "goo" was off the fiberglass. Pictures in the above post of the original problem. We are guessing it was a combination of sunscreen products. That is just a guess based on the fact that goof off pro strength took it off with some vigorous rubbing. Then had to go back with the muriatic acid as the "goo" had trapped iron stains behind itself. So the pool surface looks like new. Water is being trucked in today. I read as much as i could in the forum articles about iron. I have never had brown water from Iron. Water has been crystal clear for 3 seasons. I talked to our water softer technician and he said my iron level when tested is less than 1ppm. I am going to have to top off with my well. So, last questions are:
1. should I go ahead and proactively treat my water up front and weekly for this trace amount of soluble iron?
2. Is there a product that can help mitigate sunscreen products from accumulating on the fiberglass? (If that is indeed what that was)
3. I looked at the article with the big blue filter set ups on the fill hose. I like the idea as it is cheaper and easier than a whole house ionization system for iron. (Which the company that sells them around here said i don't need based on water sample)
Has anyone else besides the original poster of that set up used it with any success?