Should I be worried about "slimy" gunite boulders?

[JayBauman]

My pool was built last winter, and I started filling in early December. I have followed TFP methodologies since Day 1...I even had my TF-100 test kit before we started filling. I do the full suite of testing every Friday, and a few times a week I use the Taylor K-1000 to check chlorine (orthotolidine) and pH. Other than some pH and alkalinity excursions during the initial days right after filling, I am not aware of any time that my chemistry has been "out of whack" (according to TFP recommendations), and I've never seen my TC drop below 3. My pool has been clean and sparkly since Day 1--even my fill water was perfectly clear!

I don't have a "traditional" in-ground pool with waterline tile; instead, I have gunite boulders that roll from my decking into the water, which make for a lagoon-type of vibe. (Check out my build thread if you want to see what I'm talking about.) Do to the design, it's hard to use my pole brush to clean the boulder waterline. Instead, I use a small hand brush and clean the waterline boulders when we're swimming. Recently, when I brush this area, I see a brief amount of brown cloud that quickly dissipates. This cloud seems to be the same color as the brownish dye in my gunite boulders. If I run my hand over some of the nooks and crannies, it can sometimes feel something a bit slimy. A few days after brushing all of this away, it seems to come back.

So I know what you're thinking right now: "This Bauman guy is another one of those pool owners who can't possibly imagine that his pool has algae." But please hear me out...while I cannot imagine how any algae found the opportunity to take over, I am fully open to the possibility that I might be suffering from this malady. But before admitting my pool care failures to the entire world, I've been trying to self-diagnose my problems. I thought I might SLAM my pool just to be sure, but I'm not sure how I know when I'd be done since I already pass all 3 indicators:

• My pool is currently perfectly clear
• CC is 0 (I've never measured anything greater than 0.5)
• Passed OCLT (I had zero loss between last night at 11:00pm and this morning at 5:00am)

Does anybody have any idea what this could be, or is this something I shouldn't even worry about? And what would be the purpose of doing a SLAM, since I already pass the requirements?

Oh yeah....before I forget. Here's what inquiring minds want to know:

PARAMETER	LAST MEASUREMENT	TYPICAL RANGE for my Pool
TEMP	90°F	85° - 92°F
pH	7.5	7.5 - 7.8
FC	15.5*	4 - 6
CC	0	0 - 0.5
CYA	70	60 - 80
TA	80	70 - 80
CH	300	275 - 300

*I raised my FC before the OCLT. I know I wasn't at SLAM levels, but I wanted a bit more resolution during the test. Last night it took 31 drops for the vial to get completely clear, and this morning it also took 31 drops.

 

[Texas Splash]

Well let's cover the most important thing first .... that is a gorgeous pool. Wow. Okay, a couple things do come to mind (mine anyways):
- When you do the OLCT (even though you passed), it is important to take it up to its full SLAM level to receive an accurate reading. The fact that you were not quite that high and still passed may not be a huge factor right now, but is something to keep in mind for later.
- I have a light-brown grout line around my pool that meets-up with the flagstone I have. If I rub it, I suspect I will get some discoloration to come-off as well. I think that is normal. In addition, I have a fountain (large pot) that serves as a type of spillway into my pool. I will get a hint of green moss around that area if it stays wet. When we have our very humid TX summers, it can be more prevalent there or around my waterline in some areas.

People with water features or rocks that are near the waterline can face challenges other don't have. At least your water chemistry does not appear to be effected, so the most important thing at this point would be continued preventive maintenance to ensure none of that slimy stuff can transfer active material to your water. The brushing is fine, and I know some people will use spray bottles with a bleach mixture to neutralize anything in those tight areas as well.

As long as your water chemistry is good, I don't think you need to worry too much at this point other than preventive maintenance. Others may have a suggestion or two, and I hope you have a great summer.

 

[JayBauman]

Well let's cover the most important thing first .... that is a gorgeous pool. Wow. Okay, a couple things do come to mind (mine anyways):
- When you do the OLCT (even though you passed), it is important to take it up to its full SLAM level to receive an accurate reading. The fact that you were not quite that high and still passed may not be a huge factor right now, but is something to keep in mind for later.
- I have a light-brown grout line around my pool that meets-up with the flagstone I have. If I rub it, I suspect I will get some discoloration to come-off as well. I think that is normal. In addition, I have a fountain (large pot) that serves as a type of spillway into my pool. I will get a hint of green moss around that area if it stays wet. When we have our very humid TX summers, it can be more prevalent there or around my waterline in some areas.

People with water features or rocks that are near the waterline can face challenges other don't have. At least your water chemistry does not appear to be effected, so the most important thing at this point would be continued preventive maintenance to ensure none of that slimy stuff can transfer active material to your water. The brushing is fine, and I know some people will use spray bottles with a bleach mixture to neutralize anything in those tight areas as well.

As long as your water chemistry is good, I don't think you need to worry too much at this point other than preventive maintenance. Others may have a suggestion or two, and I hope you have a great summer.

Your comments made me realize that I wasn't clear on one thing: The "slimy" feeling is below the water line. Everything above appears/feels completely clean.

 

[Texas Splash]

Hummm, that is odd. Slimy in that area (under water) would not be ideal. I know we can have algae even with no CC, and sometimes we can be mislead by an OCLT if not done properly or the counts were off - not saying your was, it just happens. I would think your OCLT would definitely show a problem with active (slimy) algae in the water. Curious, is that sliminess along the entire perimeter of your pool or does it appear isolated to just one area (i.e. due to circulation or the spa spill-over)?

 

[Tepelus]

Take a clean pipe and sample the water between the boulders. I suspect this is an area with defficient circulation and the chlorine might not be even distributed. Measure in the place where you suspect a problem.

 

[cowboycasey]

it sounds like you are fine, I like the spray bottle of liguid chlorine.. Get in there and spray while brushing that rock line once or twice a week and call it good..

The one thing I did notice is you are keeping your FC at the lower levels, you may want to keep them between 6 to 9 FC for 70 CYA.. When or if you drop to 4 you are below the recommended level of 5.. Pool School - Chlorine / CYA Chart

Maybe try those 2 things and see, you have a great plan and have been doing it all correct

 

[JayBauman]

it sounds like you are fine, I like the spray bottle of liguid chlorine.. Get in there and spray while brushing that rock line once or twice a week and call it good..

The one thing I did notice is you are keeping your FC at the lower levels, you may want to keep them between 6 to 9 FC for 70 CYA.. When or if you drop to 4 you are below the recommended level of 5.. Pool School - Chlorine / CYA Chart

Maybe try those 2 things and see, you have a great plan and have been doing it all correct

According to the table you reference, my FC range is adequate; I have SWG. Are you telling me that this table is not correct?

 

[zea3]

it sounds like you are fine, I like the spray bottle of liguid chlorine.. Get in there and spray while brushing that rock line once or twice a week and call it good..

The one thing I did notice is you are keeping your FC at the lower levels, you may want to keep them between 6 to 9 FC for 70 CYA.. When or if you drop to 4 you are below the recommended level of 5.. Pool School - Chlorine / CYA Chart

Maybe try those 2 things and see, you have a great plan and have been doing it all correct

According to the table you reference, my FC range is adequate; I have SWG. Are you telling me that this table is not correct?

Cowboycasy and JayBauman, there are different recommendations for SWG vs manually chlorinated pools. I think Cowboycasy missed that you have a SWG. The daily target for a pool with a SWG and CYA of 70ppm is 3-5ppm FC.

JayBauman did you turn off the SWG for the OCLT? How far below the waterline does the slimy feel extend? Do you have a lot of sunscreen users in the pool?

 

[Chrissykr]

I have a much different system than you and last year was my first year with a pool so take it with a grain of salt....

Last year I dutifully brushed my pool once a week and by the end of the week my family said my pool was slimy. This year I bought a robot and used it several times a week. My family said the pool felt much differently, almost squeaky clean and no slime. My robot didn't work out so it is sitting in the garage. Maybe those areas need more brushing?

I was doing some research a couple of weeks ago and came across some articles on biofilms and the importance on brushing and now I run the brush over the pool a couple of times of week and even with no robot for five weeks now I have had no slime.

 

[pooldv]

Hi Jay,
My bet is that it is algae getting a little start occasionally. I've had the slimy feel a few times. Probably due to slightly less circulation in the area. Brushing that area a couple of times a week will probably fix it. I have some rocks at the waterline and that is where my algae grows, in the mortar. I have a little handheld nylon brush to brush that area, but since I raised my FC a little it has stayed clear. I would raise your normal chlorine target by 1 or 2 ppm. Especially during the hot summer. Riding so close to the minimum could cause localized areas to drop below minimum especially on big swim days with lots of people swimming or long swim days.

I have 70 CYA and I keep my FC at 7-8. And often 10ish when we plan to spend all weekend in the pool. Which is every weekend!

 

[JoyfulNoise]

I have a rock waterfall and there's a small section of it with a stone ledge that is submerged, maybe ~1 sq ft of surface area. It is very easy for the small area to have stagnant water and the water volume in that area (maybe 1-1/2" deep) is so small that the FC could easily get used up with just an hour of hot sun. There is a grout line there that I have, on occasion, found green algae growth. My water otherwise is like yours, clear, no CCs and holds chlorine. So here's a few things I have done to mitigate the issue -

1. Run the waterfall 3X per day for 30mins each time to ensure adequate water exchange in that area;

2. CONSTANT VIGILANCE! (anyone get the literary reference?). I keep close watch of the suspect area to look for any signs of growth.

3. Diluted bleach spray. I have one of those one gallon garden canister sprays (the kind you hand pump) and I fill it with a dilute mixture of 4 parts water and 1 part Clorox. I make sure to spray the entire waterline of the water feature to ensure that it sees bleach. I do this at the end of the day roughly 2-3 per week during the swim season.

Anything you can do with a scrub brush will likely help. As a previous poster mentioned, submerged surfaces whether natural stone or formed from gunite, are beautiful but require additional care and attention....


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[cowboycasey]

According to the table you reference, my FC range is adequate; I have SWG. Are you telling me that this table is not correct?

I missed that, So sorry.. it is even in your sig

 

[JayBauman]

2. CONSTANT VIGILANCE! (anyone get the literary reference?).

No, Mad Eye, I don't get the reference. Can you enlighten us?

JayBauman did you turn off the SWG for the OCLT? How far below the waterline does the slimy feel extend? Do you have a lot of sunscreen users in the pool?

SWG was turned off for OCLT.
Slimy feeling is limited to the gunite boulders, which extend from 3-6" into the water, in general. There is never any slimy feeling on my plaster, and brushing the plaster does not give any cloudy residual...this is limited to boulders only.
We are a family of fair-skinned people. There's always some sunscreen getting applied (and presumably getting washed off), which is my 2nd-most favorite explanation for the slime.

Hi Jay,
My bet is that it is algae getting a little start occasionally. I've had the slimy feel a few times. Probably due to slightly less circulation in the area. Brushing that area a couple of times a week will probably fix it. I have some rocks at the waterline and that is where my algae grows, in the mortar. I have a little handheld nylon brush to brush that area, but since I raised my FC a little it has stayed clear. I would raise your normal chlorine target by 1 or 2 ppm. Especially during the hot summer. Riding so close to the minimum could cause localized areas to drop below minimum especially on big swim days with lots of people swimming or long swim days.

Brushing it is not a problem; that's what I'm doing now. I was just wondering if I somehow had missed something.

I could imagine that low circulation in localized areas could allow algae to get a toe-hold. However, I also find slimy areas on my skimmer inlet areas, which should be the most circulated parts of my pool. The next-highest area is near my boulder waterfall, which gets run every day. I would not expect this area to be stagnant. The biggest problem is on the boulders on my sun shelf. This never feels slimy, but gives the most amount of cloudiness when I scrub it. You might argue that this is an area with low circulation, but my in-floor cleaning system keeps this area stirred up for multiple hours per day.



Thanks, everyone, for chiming in (and please continue to add comments if you think of something else....). I don't see anything here that suggests I need to do something differently. I'll keep chlorinating and brushing to keep everything at bay. I wonder what happens when my water temperature drops back into the 70s. I didn't really have any observable slimy areas then.

 

[Texas Splash]

The only other thing I was thinking of earlier while reading all the replies was the material your PB used. By any chance have you considered contacting the builder to ask if there has been any history of that specific product used to fabricate the boulder molds of becoming slimy and not responding to standard chlorination or algae treatments? Just a thought.

 

[JayBauman]

So I brought my pool up to SLAM levels and passed all 3 requirements on the first night. The only thing I've noticed is that the places where the "slimy feeling" accumulates is exactly where the pool rocks/water get the highest temperature. Between my waterfall, spill-over spa, and in-floor cleaning system, I have quite excellent circulation in the pool. Whatever is happening is quickly eliminated by brushing. I can live with that. My wife, on the other hand, would never let me forget it if the pool turned green!

 

[kimkats]

LOL Wife leave Jay alone! He is doing a great job so there! LOL

Kim

 

[pooldv]

Well, you are a looong way from a green pool. A month ago I had algae in the light, the pool vac and a dozen or so spots around the pool. My CC was 0 and water was as crystal clear as it has ever been. Never even a hint of cloudiness.

Maybe there is something about those rocks that attracts or holds the sunscreen. None of us ever use sunscreen so I don't really know how it acts.

 

[JoyfulNoise]

Unfortunately when you have irregular surfaces around your pool, water chemistry variations are always possible. Rock waterfalls (I have one) can be fun and beautiful, but they typically require extra care and maintenance to keep them clean. Stagnant water and damp porous surfaces are the enemy you typically have to fight against.


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[JayBauman]

Update: My pool was "slimy" in the usual locations, even after the SLAM. After daily brushing for a few days afterwards, the slimy feeling went away and hasn't returned. We were using the pool less during these times, so maybe I'll chalk it up to sunscreen. Nothing about this situation is consistent with algae, so I'll assume that I was fighting the wrong problem. I did, however, get the opportunity to learn how to read the born-on dates on bleach jugs.

 

[JoyfulNoise]

Update: My pool was "slimy" in the usual locations, even after the SLAM. After daily brushing for a few days afterwards, the slimy feeling went away and hasn't returned. We were using the pool less during these times, so maybe I'll chalk it up to sunscreen. Nothing about this situation is consistent with algae, so I'll assume that I was fighting the wrong problem. I did, however, get the opportunity to learn how to read the born-on dates on bleach jugs.

Funny story I've told before - I have a sister-in-law and brother that visit annually around April/May timeframe. They're east coast city-slicker DINKs (dual-income, no kids). My SIL loves the sunshine here in AZ and uses our pool as an excuse to work on her pre-summer tan for all her NYC fashionista colleagues. I swear the woman goes through two full bottles of tanning lotion (mostly oil with a tiny amount of SPF to it) during their stay. My pool water surface looks like the shores of Alaska after the Exxon-Valdez disaster. I bought a 500-ct box of PigMat Oil Absorbent polypropylene cloth that I float on the pool surface and stuff in the skimmer to soak up the hydrocarbons. The first year I did not do that and I had a thick scum-line all around the pool. I literally has to drop the waterline an inch or two and then scrub it off to get my clean tiles back. So yeah, suntan lotion can definitely cause you headaches.


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