Strange FC Readings During Slam

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M

mbeavers1

Well-known member
Sep 10, 2019
89
Houston, TX
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
When I started my Slam I had a FC of 0 and CC = 1.5. I followed process, testing 3x daily and brushing/vac. I was almost there CC= 0 and OCLT = 1.5 and I ran out of liquid CL. It sat for 1.5 days and FC dropped off to 2.5.

Today, I resumed after lunch. I added 2.5 gal per Pool Math to get to 16 (CYA = 40) and then checked it about 4 hours later. FC only rose to about 6.5 - 1st wierd reading cuz my Pool Math is calibrated. Think nothing of it and add 2 gal of liquid to get it to 16. I just checked it (abt 4hrs later) and it was only at 9.2! I added another 1.5 gal just now but since 1pm (8hrs total) today I have added almost 6 gal of chlorine to get from 2.5 to 16.

Per PM, my FC should be almost 35!! I checked the age of my reagents and dates are 5/22. I use a Taylor DPD kit and a speed stir - never had probs before. My water is crystal clear with nothing green in sight and it was brushed and vac'd after 1st add today.

Now....the liquid I used was not from my usual place but it was Hasa and 12.5%. I confirmed that PM was using the right concentration.

What gives? Any ideas?
 
proavia said:
Old chlorine (even if it's Hasa it could have been sitting at the retailer), high chlorine demand, testing error are 3 things that come to mind.
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Yup. I cant see the last 2 because:

1) I was most of the way through the slam. OCLT was 1.5-2 before my break. FC never dropped below my min for a CYA of 40. So how could my CL demand be THAT high.

2) Very familiar with test. 2 scoops dry into 25mL, turned red, added drops 1 sec apart til it went clear. Even repeated test with different chems and got same number.

It has to be old Cl...Dang it that sucks. Liquid is $$$ now. 8 bottles for $90.
 
Last edited by a moderator:
If using the 25ml water sample, each drop counts as 0.2
If using the 10ml water sample, each drop counts as 0.5

Based on your statement earlier of losses that ended in ".5" and your last statement of using the 25ml sample size, something doesn't add up.

A lot of stuff can grow in a day.

But my first guess of old chlorine is probable.

Using the 10ml sample saves reagents. Many only use 25ml for the Overnight Chlorine Loss Test - but 10ml is good enought there too.
 
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mbeavers1 said:
It has to be old Cl...Dang it that sucks
Click to expand...
Know how you should have known ? When you verified you reached your target after adding. If things are going great in a slam, then save the reagents, but once it gets screwy, go back to verifying you hit target.

You will want to with your daily dose as well, because if the dose doesnt do what you thought it did, you'll be SLAMing again.
 
During my first slam, I was using 1-2 gallons per 2-4 hours. I'm not surprised. Went through 30-45 total gallons. Granted, 30K gallon pool, but it can consume. Go to my pool logs around the end of June/early July. 120-240 ounces every 2-4 hours. The longer the slam goes, the more it will take. If you can check every 2 hours it will go faster.
 
mbeavers1 said:
It sat for 1.5 days and FC dropped off to 2.5.
Click to expand...
mbeavers1 said:
Yup. I cant see the last 2 because:

1) I was most of the way through the slam. OCLT was 1.5-2 before my break. FC never dropped below my min for a CYA of 40.
Click to expand...

FC of 2.5 is below minimum for CYA of 40.

You can always test the strength of your chlorine by diluting 10,000 to 1 - Put 1ml in 100ml of distilled water, mix well, then take 1ml of that and mix into another 100ml of distilled water. Then sample this mixture normally. Whatever ppm you get as a result is equal to the percentage in your jug.
 
Test your FC 15-30 minutes after adding the liquid chlorine to determine what FC was really added.

Checking hours afterwards could mean you have algae consuming the FC during that time period.
 
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This SLAM has been challenging. Finally last night I passed all the criteria. My OCLT results were 0.8 and my CC =0, water crystal clear....done, right?

My FC was still above my shock level so I wanted to get a good idea what my chlorine consumption was going to be so I could get started with my new SWG. I let the pool keep running all day but did not brush, vaccum, or add any liquid. Tonight I went to check my FC. My FC dropped from 18.8 this morning to 11! Also my CC was 1.5ppm. It was cloudy all day and cool. Am I crazy to think that I may not be done?
 
I am still going on this SLAM and am starting to think possibly I am doing something wrong.

I have checked my CYA level and its between 30 and 40...can barely see dot at 30, so rounded up to 40. My SLAM FC level is 16.

I have the Taylor 2005 kit. Normally, i use 10mL of water, 2 scoops of powder, and the speed stir.

When adding the 871, I add drops 1 at a time roughly 1 sec apart until the water goes from pink to clear then calculate. I have noticed that if I let the sample spin a while longer it goes back pink. Am I not waiting long enough between drops?

I am checking FC every 2-4 hours, brushing/vaccuming 1x per day. My CC has ranged from 0 to 1.5ppm and my OCLT last night dropped 1.4ppm. This tells me to keep going.

I continued until 3 nights ago I passed all criteria so I stopped for 1 day. I noticed FC dropping fast so checked CC and it was back to 1.5.

I started the whole process again...my water is crystal clear, I have checked the bottom of all my ledge loungers, in the skimmers, no traces of anything green.

I realize that this takes awhile but Im 1.5 weeks in and have never had any visible green. I just wanted to make sure that everything was dead before starting raising my CYA to start my new SWG.

My pool is 23k gallons and in 1.5 weeks I have dumped in almost 40gal of liquid trying to get this thing finished!

What else could I be missing?
 
Once the test sample turns clear , the test is over.
Clean your test vial. Use alcohol or bleach.
 
wireform said:
When was the last time you broke open the filter. It's probably very dirty or at minimum algae laden.
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Filter could 100% be the issue. We just finished pollen season here in Houston and I havent cleaned. I wanted to get through the slam then clean but I can 100% tear it apart.
 
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No need to clean it every use. But persistent CC has been resolved in the past by cleaning the test vial.
 
mknauss said:
No need to clean it every use. But persistent CC has been resolved in the past by cleaning the test vial.
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Soo....good call on the alcohol. CC was at like 1.5ppm 2 hours ago and is now at 0! Filter is clean and FC is at 17.2. Will run an OCLT tonight and see what happens.
 
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Ok. Think I finally passed....again. OCLT = 0.4ppm and CC= 0.4 ( been bouncing between 0 and 0.4 - almost clear on 1 drop, 2nd drop w/25ml is clear).

Think I will keep adding CL today to make sure today, but do you all think its safe to increase my CYA from 30ish to 70 to get my swg % dialed in?

I dont want a repeat where I passed 1 oclt and started over 🤣
 

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