FC low after attempt at SLAM

IceShadow

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Jun 8, 2019
3,972
Milwaukee, WI
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Something to consider too is that adding LC does add salt. It's not a ton, but if you ad a LOT of LC, it could push your salt levels up to where you have to partially exchange anyhow.
 

barbc2000

Active member
May 16, 2022
31
East Longmeadow MA
Pool Size
26700
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45
FC will eventually overtake whatever is in the water if you add enough of it.

The danger is we can't say how much that will be because we don't know what's in the water. Something is there that is consuming FC. It's also being consumed by the FC, but we don't know how much of it is there.

So - you can either follow the protocol for Ammonia (which is to keep adding 10 FC at a time and retesting, repeat until FC holds) or you can exchange the water out. I have to imagine that the costs for the water exchange might be less, depending on what it costs to fill the pool. If you do drain, I would do a No-Drain Water Exchange to avoid potentially shifting the liner. Here's info on that: Draining - Further Reading .

Which way to go depends on your cost of water and how lucky you feel. It could be the next 10ppm you put in finishes off what's in there and you hold chlorine fine. Or it could be dozens and dozens of chlorine jugs. Changing out the water is going to be more certain of a cost you can know, but will cost more than adding jugs if the next one would have been the last. Ultimately it's your call on which way to go.
Okay, I might be miss understanding you:).

When you say keep adding 10FC, what does that mean. One gallon of 10% liquid chlorine?
Namco had 12.5% liquid chlorine. Would that be better?
Namco also had chlorine granules bag that were 80%. Is that better?

Sorry for so many questions.
 

Wobblerlorri

Bronze Supporter
Apr 16, 2019
2,012
Bremen, GA, 65 m west of Atlanta
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Okay, I might be miss understanding you:).

When you say keep adding 10FC, what does that mean. One gallon of 10% liquid chlorine?

No, it means add sufficient liquid chlorine to bring your pool FC up to 10 ppm.

Namco had 12.5% liquid chlorine. Would that be better?

You'd use less because it's stronger. You'd still be adding enough to bring you up to 10 ppm FC.

Namco also had chlorine granules bag that were 80%. Is that better?

No!! Don't use that!! You'd be adding other additives that could affect your water!!

Just add enough FC to bring you up to 10 ppm, and keep it there. The more often you can test and add the quicker this part will go. Once you reach 10 ppm and it stays there, you can do a SLAM Process.
 
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IceShadow

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TFP Guide
Jun 8, 2019
3,972
Milwaukee, WI
Pool Size
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If your pool is 26700 gallons, using the link at the bottom of this page (Old PoolMath Webpage), put in the pool size. Put current FC at 0 and target at 10.

If you use 10% chlorine (liquid chlorine and bleach is the same thing), it would be 2.75 gallons (2 gallons, 3 quarts) to add 10ppm of FC to the pool. If you use 12.5%, it is a little over 2 gallons (2 gallons and 2 cups). Which to use is going to depend on your cost and availability. If they're roughly the same cost the 12.5% is a better deal, assuming they're both fairly freshly made.

Don't use granules. That is going to add either CYA or CH to the pool, which you don't want to do now.

If your water is cheap, exchanging it out may be a better option, but chlorine will eventually overcome whatever is in the pool. We just have no idea how much chlorine it will take because we can't tell what chemical someone put in the pool is using it up. It may be something that you need to drain to get rid of anyway. Are you on municipal water, or well water?
 

barbc2000

Active member
May 16, 2022
31
East Longmeadow MA
Pool Size
26700
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45
No, it means add sufficient liquid chlorine to bring your pool FC up to 10 ppm. Each 5.5 oz of 10% LC raises your FC 1 ppm. So to get from 0 FC to 10 you would add 55 oz or 3 cups 7 oz of LC.



You'd use less because it's stronger. You'd still be adding enough to bring you up to 10 ppm FC.



No!! Don't use that!! You'd be adding other additives that could affect your water!!

Just add enough FC to bring you up to 10 ppm, and keep it there. The more often you can test and add the quicker this part will go. Once you reach 10 ppm and it stays there, you can do a SLAM Process.
So I have been trying to raise my FC. I added 10 gallons of LC and it raised it from 0.5 to 1.5. So to get to 10 is going to take 90 gallons??? Or is it not a 1:1 ratio? LC will raise it faster once it hits a certain threshold?
 

Majindro

Member
May 25, 2022
12
Michigan
Pool Size
22000
Surface
Vinyl
Chlorine
Liquid Chlorine
So I have been trying to raise my FC. I added 10 gallons of LC and it raised it from 0.5 to 1.5. So to get to 10 is going to take 90 gallons??? Or is it not a 1:1 ratio? LC will raise it faster once it hits a certain threshold?
I'm not a pool expert, but I just had this issue where I kept adding chlorine and measuring and my number never went up. I went through the 8 bottles I bought in the first 2 days and never saw the FC go up. So I went and bought another 16 bottles and kept dumping 2 bottles in and measuring 20 minutes later until it finally started to climb. I think my total amount poured in before the FC started to register was 16. No idea what was causing it, but whatever it was, the chlorine finally won the battle. Then it took 4 more bottles to get it to SLAM level and over night it only dropped 3ppm which means I'm still killing stuff, but at least there's a measurable FC level now. So just sharing my experience that I just had the same issue and eventually the chlorine did win.
 

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jeffchap

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Jun 26, 2012
2,351
Edmond OK
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Something is not right here. Do you have a cheap OTO drop test you can use? We don't normally recommend them because they only measure TC and only up to 5 ppm. But it would be useful to compare to the results of your FAS-DPD test. Maybe your powder is bad.
 

IceShadow

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Jun 8, 2019
3,972
Milwaukee, WI
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Something is not right here. Do you have a cheap OTO drop test you can use? We don't normally recommend them because they only measure TC and only up to 5 ppm. But it would be useful to compare to the results of your FAS-DPD test. Maybe your powder is bad.

I have tried the color comparison test to check. It confirms the same low FC.
 

barbc2000

Active member
May 16, 2022
31
East Longmeadow MA
Pool Size
26700
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45
I'm not a pool expert, but I just had this issue where I kept adding chlorine and measuring and my number never went up. I went through the 8 bottles I bought in the first 2 days and never saw the FC go up. So I went and bought another 16 bottles and kept dumping 2 bottles in and measuring 20 minutes later until it finally started to climb. I think my total amount poured in before the FC started to register was 16. No idea what was causing it, but whatever it was, the chlorine finally won the battle. Then it took 4 more bottles to get it to SLAM level and over night it only dropped 3ppm which means I'm still killing stuff, but at least there's a measurable FC level now. So just sharing my experience that I just had the same issue and eventually the chlorine did win.
This is good to hear! I added another 10 gallons tonight. First 6 gallons and tested 30 minutes later. FC 1.5. Went out and came home and added another 4 gallons. Tested right after adding the chlorine and FC was 9! So the chlorine is good. I'll see what it is in the morning.
 
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IceShadow

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This is good to hear! I added another 10 gallons tonight. First 6 gallons and tested 30 minutes later. FC 1.5. Went out and came home and added another 4 gallons. Tested right after adding the chlorine and FC was 9! So the chlorine is good. I'll see what it is in the morning.
Getting a reading is good! You may have consumed whatever was in the water eating up your FC.
 

PoolStored

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Back down to 0.5 this morning. Have added a total of 20 gallons. I guess I will buy 10 more and see what happens.
So you likely had Ammonia, and now you have algae. Just follow the SLAM Process process from here out.

I used 45 gallons for my slam, and I didn't have ammonia. You will get this!
 
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barbc2000

Active member
May 16, 2022
31
East Longmeadow MA
Pool Size
26700
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45
So you likely had Ammonia, and now you have algae. Just follow the SLAM Process process from here out.

I used 45 gallons for my slam, and I didn't have ammonia. You will get this!
45 gallons! Well thank you for that information. I will go buy 25 more gallons. The slam process says to not test more than once an hour.

So how much chlorine should I add at a time and test how often. Also, I do this in the evening, right?
 

PoolStored

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Jun 24, 2021
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Ashtabula, OH
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45 gallons! Well thank you for that information. I will go buy 25 more gallons. The slam process says to not test more than once an hour.

So how much chlorine should I add at a time and test how often. Also, I do this in the evening, right?
No need to test more than once an hour. Test your FC. Use pool math to calculate how much to add to get back to your SLAM target.

Do it all day long. If you can do every 1-2 hours, it will go faster.
 

IceShadow

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Jun 8, 2019
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Milwaukee, WI
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45 gallons! Well thank you for that information. I will go buy 25 more gallons. The slam process says to not test more than once an hour.

So how much chlorine should I add at a time and test how often. Also, I do this in the evening, right?
Basically, test, then add back to SLAM target. Your target with a CYA of 60 is 24ppm per the FC/CYA Chart. So if you test at 0ppm, you put 0 in Pool Math, put 24 for the target, put in the strength of the chlorine you're using, and it will tell you how much to add for your volume of pool. In an hour, if you test and it's 21ppm, you put 21ppm in the current, 24 for target, and it will tell you how much to add to get 3ppm more added. Repeat as often as you can, brush and vacuum often. Test and add at least 2-3 times a day, up to once an hour. The more you can do it the faster it will go. Taking a break to do things like sleep is fine - you'll just get back to it when you get up.

If your water is already still clear with no signs of algae, then really you're just looking to see if it drops overnight, between when you go to bed and when you wake up. If it doesn't, then you're done and you can let the FC drift back down to about 7-9. Test daily to make sure it stays in that area. Don't ever let it get below 5, because that's when you can get algae growing.

Let us know how it goes!
 

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