First Ever Coliform Positive Sample 😔

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Endro32

Endro32

Well-known member
Jul 1, 2021
52
Rives Junction, MI
Pool Size
60000
Surface
Plaster
Chlorine
Liquid Chlorine
As a licensed summer camp, we're required by the Michigan health department to submit weekly pool water samples for coliform testing. Since I've taken over the pool management, I've had 24 consecutive clean water samples over the course of three summers. And this week, on the second to last sample of this summer, I got a coliform positive test.

Feeling pretty discouraged now that my perfect record is no more. Tried to pinpoint all the possible causes... I've kept the FC above the minimum recommended by PoolMath, though this summer I've been doing this by adding bleach first thing in the morning (as opposed to twice a day in years past) so I usually find it having sat all night long pretty close to the minimum. We also took the sample about 15 hours after having kids in the pool. I would have thought that was long enough for chlorine to kill anything off, but perhaps not. I had one point a few weeks ago where I found the FC at 1ppm in the morning (due to a miscommunication with our lifeguard where bleach wasn't added when I thought it was). I don't know if coliform is like algae and can start growing after that and continue until a SLAM, but I suppose that's another possible cause. Our fill water (well water) also has a TA of about 450, so I've been keeping the pH around 7.8 so I don't have to add acid as often. I know that's well within limits, but since chlorine effective goes down with higher pH and I'm running a commercial pool, I wonder if I need to keep the pH lower as a result.

Regardless, I've SLAM'd the pool, boosted the filtration with DE (had to backwash 12 hrs later), and will go back to my twice a day bleach routine to keep the FC towards the high end until we can get a SWG installed. So that should bring it back in line, but I'm hoping someone more experienced might have an idea on how I can prevent this from happening again, or if it's just to be expected from time to time.

For reference, my average test results are:
CYA: 35-40
FC: 3-7
pH: 7.6-7.8
TA: 110-130
CH: 280
 
Endro32 said:
As a licensed summer camp, we're required by the Michigan health department to submit weekly pool water samples for coliform testing. Since I've taken over the pool management, I've had 24 consecutive clean water samples over the course of three summers. And this week, on the second to last sample of this summer, I got a coliform positive test.

Feeling pretty discouraged now that my perfect record is no more. Tried to pinpoint all the possible causes... I've kept the FC above the minimum recommended by PoolMath, though this summer I've been doing this by adding bleach first thing in the morning (as opposed to twice a day in years past) so I usually find it having sat all night long pretty close to the minimum. We also took the sample about 15 hours after having kids in the pool. I would have thought that was long enough for chlorine to kill anything off, but perhaps not. I had one point a few weeks ago where I found the FC at 1ppm in the morning (due to a miscommunication with our lifeguard where bleach wasn't added when I thought it was). I don't know if coliform is like algae and can start growing after that and continue until a SLAM, but I suppose that's another possible cause. Our fill water (well water) also has a TA of about 450, so I've been keeping the pH around 7.8 so I don't have to add acid as often. I know that's well within limits, but since chlorine effective goes down with higher pH and I'm running a commercial pool, I wonder if I need to keep the pH lower as a result.

Regardless, I've SLAM'd the pool, boosted the filtration with DE (had to backwash 12 hrs later), and will go back to my twice a day bleach routine to keep the FC towards the high end until we can get a SWG installed. So that should bring it back in line, but I'm hoping someone more experienced might have an idea on how I can prevent this from happening again, or if it's just to be expected from time to time.

For reference, my average test results are:
CYA: 35-40
FC: 3-7
pH: 7.6-7.8
TA: 110-130
CH: 280
Click to expand...
Did you test the water around the same time as the offending sample was taken? FC down to 1ppm and then offending sample taken after a bunch of kids swimming sounds like two potential roads to investigate.
 
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Bperry said:
Did you test the water around the same time as the offending sample was taken? FC down to 1ppm and then offending sample taken after a bunch of kids swimming sounds like two potential roads to investigate.
Click to expand...
I did, actually. The FC was was at 3.5ppm at the exact time the sample was taken. CYA was about 30.

As for it dropping to 1ppm, we've had a couple samples taken since then that both tested clean before this one. So definitely concerning, but hard to pinpoint if that was the cause.
 
Edit to fix after seeing you do have well water. Do you have well water? If so, have it tested. Coliform comes from soil contamination. Most varieties harmless, but not all. Here on the flatland coast, 80% of wells would at some point test positive for coliform, especially one that's opened for repairs a lot. It just happens. My well is but 5 years old, 450 feet, I've had a case of it. Most likely introduction was the drill stem when the well was dug had carried it in, layed on ground, etc.... I make it a point to shock my well periodically. My outofill for pool gets a colony now and again if I don't keep a piece of tab in it.
 
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I can’t add much other than just sort of observing that 15 hr CT with FC > 10% CYA gets me to wonder if something other than bather load as source of the coliform. Could be just a flock of geese or seagulls did a flyover just before the sample was taken? Or as Toxophilite says, the make up water?
 
SoDel said:
I can’t add much other than just sort of observing that 15 hr CT with FC > 10% CYA gets me to wonder if something other than bather load as source of the coliform. Could be just a flock of geese or seagulls did a flyover just before the sample was taken? Or as Toxophilite says, the make up water?
Click to expand...
Coliform is bacterial. It exists everywhere in nature, even within us in our guts. It's not a singular bacteria, it's a whole gambit. Majority harmless, but e-coli is a coliform bacteria, and one of the very few that are harmful to us. A coliform test is basically a sanitation level test, as well as a contamination source test. The presence of any, which will be more than likely harmless, indicates that an "condition" exists in our sanitation maintenance. Could be a lack of, or, could be a source introduction.
 
Toxophilite said:
Coliform is bacterial. It exists everywhere in nature, even within us in our guts. It's not a singular bacteria, it's a whole gambit. Majority harmless, but e-coli is a coliform bacteria, and one of the very few that are harmful to us. A coliform test is basically a sanitation level test, as well as a contamination source test. The presence of any, which will be more than likely harmless, indicates that an "condition" exists in our sanitation maintenance. Could be a lack of, or, could be a source introduction.
Click to expand...
Yes, I see. All I’m trying to get at is seems like it may have been introduced, from whatever source, close in time to the test sampling just kind of noodling, if I understand it correctly, CYA of 30 and FC of 3.5 with the water sitting with no bathers for 15 hrs. Coliform also exists in bird guts and around here there’s enough bird poop that runs into the ocean after heavy rains to render the ocean, which is not sanitized of course but is an awful lot of water, a hazard to bathers. Just got me to thinking maybe birds pooping in the water near the sample time and not something the OP did or didn’t do.
 
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SoDel said:
Yes, I see. All I’m trying to get at is seems like it may have been introduced, from whatever source, close in time to the test sampling just kind of noodling, if I understand it correctly, CYA of 30 and FC of 3.5 with the water sitting with no bathers for 15 hrs. Coliform also exists in bird guts and around here there’s enough bird poop that runs into the ocean after heavy rains to render the ocean, which is not sanitized of course but is an awful lot of water, a hazard to bathers. Just got me to thinking maybe birds pooping in the water near the sample time and not something the OP did or didn’t do.
Click to expand...
I follow you! This thread reminded me to shock my well again, due, so working on that now.
 
Sorry your perfect record has a mark on it 😩
pools unfortunately are in a constant battle with nature’s nasties.
sounds like the synopsis here is:
1. Dose twice daily to ensure you don’t broach minimum at any time.
2. Treat your well to ensure you’re covered there - not just because of the pool top off situation but for potable water purposes as well.
Good luck with the rest of your summer & all those kiddos! 🍀
Curious- What kind of set up might you be able to get for a 60,000 gal pool? We always recommend something rated for at least 2x’s your pool’s volume but that sounds like some large cells!
I would love to see the set up when the time comes!
Here’s a thread on some commercial options.

Commercial Pool Conversion

I am working on behalf of my HOA to determine the cost of converting our 2 pools from traditional chlorine to SWG. Our main pool is 150,000 gallons. I understand that I need 2x the rated chlorine generation/day (i.e. build out for a 300,000 gallon pool) but I'm having a tough time determining...
www.troublefreepool.com www.troublefreepool.com
 

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Please keep in mind that TFPC is designed for residential pool care, where the main culprit for chlorine consumption is UV.

This is different in a public pool setting with potentially high bather load. A few doses of urine, and your FC is gone.

Just testing and dosing in the morning is not enough. Letting FC sit at an unknown state over night is not a good idea.

You need to test and dose multiple times throughout the day. This also helps to minimise the impact of things going wrong or miscommunication. If one test gets missed for whatever reason, the water may stay untested for 48h with testing once a day only. This time gets drastically reduced by testing multiple times a day.

What are your locally applicable regulations for pH, CYA, CC (or TC) and min/max FC?
 
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Mdragger88 said:
Curious- What kind of set up might you be able to get for a 60,000 gal pool? We always recommend something rated for at least 2x’s your pool’s volume but that sounds like some large cells!
I would love to see the set up when the time comes!
Click to expand...
I've been looking at a Pentair COMSYS system. The COMSYS-8 seems to be capable of handling our chlorine demand with 50% output at 12hrs of pump runtime per day, even though they spec it as a 40,000 gallon unit. It's not that much more expensive for the COMSYS-12, though, so we may go that route just to ensure we definitely have enough capacity.

mgtfp said:
Please keep in mind that TFPC is designed for residential pool care, where the main culprit for chlorine consumption is UV.

This is different in a public pool setting with potentially high bather load. A few doses of urine, and your FC is gone.

Just testing and dosing in the morning is not enough. Letting FC sit at an unknown state over night is not a good idea.

You need to test and dose multiple times throughout the day. This also helps to minimise the impact of things going wrong or miscommunication. If one test gets missed for whatever reason, the water may stay untested for 48h with testing once a day only. This time gets drastically reduced by testing multiple times a day.

What are your locally applicable regulations for pH, CYA, CC (or TC) and min/max FC?
Click to expand...
I know I'm a bit of an oddball on here because of that exact reason. I've always found the chlorine demand to be a pretty consistent 4ppm per day, though, even on weekends when nobody is in the pool (even if I bring it to SLAM level on Friday and pass the OCLT the following morning). So our bather load actually seems relatively low for a non-residential pool, and I've never struggled to keep the FC exactly where I want it. Truth be told, I just got lazy and tried to maintain it with one dose per day rather than two.

Michigan EGLE actually has water quality standards that are basically in line with TFP knowledge (rather than pool store knowledge), and specify that with a CYA of 20-40ppm, the FC level should be a minimum of 2.0 if the pH is 7.2-7.5, and a minimum of 4.0 if the pH is 7.5 to 8.0. They don't specify a maximum.
 
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