basic free chlorine question

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geewiss

Bronze Supporter
Jul 23, 2020
48
Centreville Maryland
Not sure if this question is as basic as I think it is but here goes.

Pool was just opened by pool company. Pool was green due to mesh safety cover. Pool company put some chemicals in but I wasn't home and don't know what they put in it....I'm thinking it was some cal-shock or something. I do know that pool was green initially and a day later the green is gone but pool still needs work as it's pretty cloudy.

Here is my basic question as I'm still learning.
FC reads 0. I put in 128 oz of 10% bleach and tested 12 hours later and FC still reads 0.
PH = >8 very purple. I did 128 oz of acid it's now at 7.4
My ALK was at 90
My CYA didn't measure...guess it's 0.
Hardness = 250
Water is cold at 66 degrees and it's raining.

According to pool school 128oz of 10% should raise my FC by 3.8. see screenshot

With that information, I guess it's safe to say that i'm surely in need of a SLAM.

Thanks in advance to this awesome forum!
 

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Well, there are no actual questions in your post, but I'll give you a couple! When you added chlorine how long did you wait to test again? Do you remember what your CYA was when you closed the pool?
 
With your pH that high and CYA that low, the first thing I'd do is an ammonia test.

Add enough chlorine to get to 10 ppm and let that mix for about 10 minutes. Then do an FC and CC test. If your FC dropped below 5 and you have a lot of CC then hold off adding CYA until you get this fixed. Repeat that process until the FC holds above 5 ppm. Then raise your CYA level to 30 and begin the SLAM Process
 
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Ok, then you probably had a bacterial conversion consume your CYA and leave you with a bunch of ammonia. Ammonia will burn up chlorine super quick. Do the steps Donldson recommended every 10 minutes until the FC starts to hold. That is the only way to get rid of ammonia. Do not add any CYA until the ammonia is gone.
 
You need 10 ppm of FC to eliminate 1 ppm of ammonia. So assume you have 5 ppm of ammonia. Then you would need 50 ppm FC, or 10 gallons of 10% just to eliminate the ammonia. Then more for the SLAM. So 20 would be a good start.
 
I'm beginning to wonder if my R-0870 is bad. Just noticed that it's out of date (07/2021). Just as a test I took some straight 10% bleach and mixed it with water and it didn't even turn a slight bit pink.

I guess I'll order some new reagents before going any further.
 
Very high FC (as in your bleach in water test) can cause the pink to be bleached out when adding the R0870.

Is the powder dark colored? Clumped up?
 

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geewiss said:
Sorry another follow up question. For getting rid of the ammonia, I should start with raising FC to 10? And to get it to 10, I'm only going to need to add three 128oz bottles of 10% chlorine? Doesn't seem like much to start. Is this correct?
Click to expand...
Correct. And if you have ammonia, that chlorine will be instantly consumed. You test the FC again in 10 minutes. If less than 5 ppm, add 3 more gallons. Keep repeating until the FC is above 5 ppm when tested.
 
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Put in three gallons of 10% and the FC held at 10 after the 30 minutes. I'm going to test it again after another 30 minutes or so.

If it does continue to hold, I guess I can go ahead and add CYA. Then after my CYA is 30? I should go ahead and SLAM?

Am I missing anything?

I guess CYA and FC "burn" off through the winter?
 
geewiss said:
Am I missing anything?
Click to expand...
Sounds great. Get the CYA dissolving using the sock method. Go straight to SLAM. Test the CYA a day after the granules are dissolved from the sock.
The FC is consummable and is lost to UV from the sun and organics each day.
The CYA over the winter is diluted by rain/snow.
 
That is fine. If sun is shining on the pool surface, and the CYA is near 0, the half life of FC in the water is just under 1 hour.
 
Very cloudy day here so I'm not sure what happened and why it went down, unless that's normal.

I did add some muriatic acid and I'm now thinking that could of influenced the FC reading?

Isn't it going to be hard to keep the FC at SLAM level with CYA of 0? Or does it dissolve enough, quick enough to keep FC stable?

I thought I had some stabilizer but I don't....so going to the store now.

Thanks for all your input!
 
A few things. If going forward with slam the PH needs to be about 7.2 before you have 10+ on the FC. So if the FC holds as in the previous discussion then get the PH managed to 7.2 also get the CYA in for 30 ppm and start to slam assuming it's 30ppm CYA already.
 
geewiss said:
I did add some muriatic acid and I'm now thinking that could of influenced the FC reading?
Click to expand...
MA does not influence the FC reading.
geewiss said:
Isn't it going to be hard to keep the FC at SLAM level with CYA of 0? Or does it dissolve enough, quick enough to keep FC stable?
Click to expand...
At the first, your FC will be attacking organics so quickly the UV loss will not be that much of an issue. The CYA granules should dissolve quickly, especially if you squeeze the sock after they get mushy.
 

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