Green after heavy rain

[tikoh]

We got a much needed inch of rain last night, but when I looked at the pool this morning I had trouble seeing the bottom of the deep end. I tossed in the dolphin and turned the pump up and 6 hours later I'm looking pretty green.

Yesterday's Test:
FC: 4
pH: 7.2
TA: 80
CH: 50
CYA: 30

I knew we were getting heavy rain so I added half a gallon of 12.5%

This morning:
FC: 4.5
pH: 7.2

Just now after seeing how green we're looking:
FC: 4.5
CC: 0
pH: 7.2
TA: 80
CH: 50

I know the pH is a tad low (I was actually hoping the rain would help aerate), but otherwise everything looks good. I'm struggling to see how an algae bloom could have occured.

I'm in New York and the air quality here was awful last week so we didn't use the pool and I didn't brush at all, but I did keep up on the chlorine and ran the robot.

Any thoughts?

 

[dBsooner]

I’d perform an OCLT (Overnight Chlorine Loss Test) to see if you have anything growing. But let’s see what the experts say. I do know that rain doesn’t cause algae. Which a pool store recently tried to argue with me about.

 

[Newdude]

I'm struggling to see how an algae bloom could have occured.

You are playing kissy face with min. A half gallon of 12.5% is 1.7 FC for you. You're supposed to stay in, or above target range at all times.

 

[tikoh]

I’d perform an OCLT (Overnight Chlorine Loss Test) to see if you have anything growing. But let’s see what the experts say. I do know that rain doesn’t cause algae. Which a pool store recently tried to argue with me about.

Yeah, that's the plan tonight

 

[tikoh]

You are playing kissy face with min. A half gallon of 12.5% is 1.7 FC for you. You're supposed to stay in, or above target range at all times.

Target for 30ppm CYA is 3.5 ppm FC, no? With a min of 2.2ppm?

 

[Newdude]

Target for 30ppm CYA is 3.5 ppm FC, no?

Apologies. I read your CH at the bottom as your CYA. It's been a day.

But either way, if you lost clarity due to increased UV or a storm on any given day, you need to rethink your targets.

 

[JamesW]

Probably algae or maybe iron.

Pictures?

 

[tikoh]

Photos attached…this is after ~10ppm with the robot running and the pump on high for about 12 hours

 

[JamesW]

I would suspect algae and do a full SLAM.

 

[tikoh]

Photos attached…this is after ~10ppm with the robot running and the pump on high for about 12 hours

Edit: 10ppm for 4 hours

 

[Rocket J Squirrel]

Decades ago, I was a certified swim instructor at a newly-opened summer day camp in NJ. My responsibilities did not include water chemistry, which I assumed was handled by someone more expert at that.

One Monday, we came in after heavy weekend rain and the pool was pea green due to FC dilution. I became the movie projectionist for that day while folks poured in whatever chemicals. It cleared up in a day or two.

But to this day, um 40+ years later, I wonder whether that pool simply had a tab feeder. Teaching kids to swim was fun and rewarding (I got to hand out Red Cross patches at the end of the season) but water chemistry never even once occurred to me until the water went green. So yes, rain can wreak havoc with your chemical balance.

 

[tikoh]

I would suspect algae and do a full SLAM.

Yeah, I just got home with more bleach, going to bring it up to 14ish and see how it goes.

I had enough earlier today to bring it up to 10 and that seems to have held at least

 

[PoolStored]

Yeah, I just got home with more bleach, going to bring it up to 14ish and see how it goes.

You should follow this process. Print it out, read it three times, and keep it with you. Link-->SLAM Process

Your target FC for SLAM is 12, for CYA of 30. No need to exceed 12.

 

[tikoh]

You should follow this process. Print it out, read it three times, and keep it with you. Link-->SLAM Process

Your target FC for SLAM is 12, for CYA of 30. No need to exceed 12.

But no harm either though right?

My process for adding chemicals is add half and then adjust from there. However, if I’m trying to hit exactly 12ppm, I’m adding a quart of bleach, waiting, testing, adding a quart, waiting, testing…I’d rather just add two gallons see what it gets me, as long as it’s greater than 12 it works for me. I wouldn’t spike it to 20, but for me the $4 worth of bleach I’m wasting is worth the time saved. Or am I wrong? Does it matter?

 

[dBsooner]

Then it’s not a SLAM… the process is the process for a reason. The math is the math for a reason.

 

[PoolStored]

But no harm either though right?

My process for adding chemicals is add half and then adjust from there. However, if I’m trying to hit exactly 12ppm, I’m adding a quart of bleach, waiting, testing, adding a quart, waiting, testing…I’d rather just add two gallons see what it gets me, as long as it’s greater than 12 it works for me. I wouldn’t spike it to 20, but for me the $4 worth of bleach I’m wasting is worth the time saved. Or am I wrong? Does it matter?

SLAM level FC is safe for people and equipment. Higher than that, it is not and you can, start to do damage to equipment and pool. Including bleaching your liner.

It does matter, it is about the time (duration), not the level. You should follow the SLAM instructions. Test FC, add to get to your target, walk away, come back in a couple hours and repeat the process.

 

[tikoh]

SLAM level FC is safe for people and equipment. Higher than that, it is not and you can, start to do damage to equipment and pool. Including bleaching your liner.

It does matter, it is about the time (duration), not the level. You should follow the SLAM instructions. Test FC, add to get to your target, walk away, come back in a couple hours and repeat the process.

I'm not saying this to be argumentative, I'm trying to understand where you're coming from...Why do you feel that over 12ppm FC at 30ppm CYA is unsafe? At those levels, HOCl would likely still be within the EPA drinking water standards, and certainly safe to swim in. Even TFP's mustard algae shock level is 18ppm FC for 30 CYA.

SLAM targets are 40% of the CYA level (2.5:1) which has approximately the same HOCl as 0.8ppm FC with no CYA. The EPA allows up to 4ppm FC with no CYA which has the same HOCl as what...130ppm FC at 30 CYA? At 300 CYA and 80deg water with a pH of 7.2, my HOCl is about 1.5% of of my FC.

@JamesW are you still here? What's your take on it?

 

[JamesW]

I would be ok at 50% of CYA or even 60% (mustard level) if that makes it easier for you.

I agree that the extra amount is not a big risk, but it does go outside the recommended levels, so you are making an informed decision and accepting the risk.

The levels are conservative by design.

I might be more aggressive to get the process done faster, but I understand and accept any additional risk that being more aggressive creates.

 

[tikoh]

I would be ok at 50% of CYA or even 60% (mustard level) if that makes it easier for you.

I agree that the extra amount is not a big risk, but it does go outside the recommended levels, so you are making an informed decision and accepting the risk.

The levels are conservative by design.

I might be more aggressive to get the process done faster, but I understand and accept any additional risk that being more aggressive creates.

Thank you for the quick response! I really appreciate it.

 

[tikoh]

Okay, the good news is that we’re getting even more rain that we desperately needed. Even with the rain the water is much more blue and you can see the bottom no problem. I lost 0.8ppm FC overnight with no CC.

The bad news is that there’s still a tinge of green…but that was to be expected. I’ll get a better look once the rain stops. In the mean time I’ll monitor FC and keep on keeping on.

Thank you everyone for your help.