FC at or near zero - Updated

skasyjan

Member
Jun 4, 2020
14
Central Indiana
Short story -
Have had our pool for 7 years going on 8 and very minimal issues.
Generally test and balance the pool myself with products from big box stores (i.e. liquid chlorine, borax, etc.)
(We do have an inline chlorinator that is used sometimes.)
32,600 gallon, rectangular, vinyl pool

This Spring, opened the pool and looked good, shocked it per normal, chlorine level dropped, had a few days of decent swimming and then Milky or Lemonade looking water...

Shocked pool again, and brought it back to normal looking, CH was insanely high though (our water is hard, but this was off the charts high)...

Refreshed the water, shocked it, balanced it, looking good... BUT...

Pool was shocked at Sunday and FC was 3 (but now I think that may have been coming down from the shock). Free Chlorine seems to be at zero. Basically if I am not shocking the pool it seems it can't maintain any FC. CC is generally at or darn near 0 as well. I thought maybe my testing skills were off so I took to local pool store. Their test came back with very similar results to mine (which might confirm I don't know what I am doing :) )...

My test first / Pool store test... (Tuesday) **
FC - 0 (perhaps 0.2) / 0
TC - 0 (perhaps 0.2) / 0
CC - 0 (perhaps 0.2) / 0
PH - 7.4 / 7.3
Alk - 115 / 110
CYA - 47 / 53
CH - 220 / 200
Phosphates - (untested) / 2049
TDS - 688 / 800
- They also tested for ammonia and that was okay

Action:
- I bumped up the Alk & PH with Walmart products
- They suggested treating the phosphates, I balked at that
- They suggested throwing a few chlorine tablets in the skimmer (thinking the chlorinator might be the issue), seemed like a bad idea
- They suggested testing the water at the pool return... I did this and it DID register FC, but ONLY if I had a testing strip basically in the return. I tried to scoop out water right next to the return and got no reading..

My test first / Pool store test... (Thursday)**
FC - 0.2-0.4 / 0.1
TC - 0.4 / 0.4
CC - 0.2 / 0.3
PH - 7.6 / 7.4
Alk - 130 / 123
CYA - 50 / 48
CH - 225 / 157(?)
Phosphates - (untested) / 2139
TDS - 672 / (untested)

- They suggested treating the phosphates, I balked at that again
- They suggested bumping the PH and Alk again, but that seems unnescessary to me
- No other clues as to why FC is where it is at, but they suggested shocking again. (They ofcourse suggest Burnout 73.)
- We have an automatic pool cover so it never really gets hit with lots of rainfall, run off, fertilizer, etc.

** I am obsessive, so my tests have been done with the Taylor Test Kit, a ColorQ test kit, Test strips (read manually), and test strips read by smart phone app. (I also have a tester for TDS which I generally use for my interior water, but I have been desperate.) And they all were about the same. The pool store used their little disk for most tests.**

Pool "looks" AMAZING, but if FC is hovering around zero that's not going to last for too long. Thoughts on most efficient course of action?
 
Last edited:

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,976
Franklin, NC
My first suggestion is to stop going to the pool store. Their only response it to sell you something, usually that has noting to do with the issue at hand..

I will tell you, it didn't get this way and it may take time to clear. But, we can teach you how to get it back in shape and keep it that way for a lot less money than the pool store.

Not much credence is given to pool store testing around here. While you would think that a "professional" would be the best, unfortunately in most cases it is quite the opposite. Between employees who blindly trust the word of chemical sales representatives and high school kids working in the pool store for the summer you end up with poor results from their testing. Plus, the results of their "testing" is used to convince you that you need to buy things. Why do you think that testing is free?

But, what can you do?? We base our pool care system on accurate testing and only adding what the pool needs, when it needs it. To do that you need your own accurate test kit. So, I have to ask - what are you using to test?

Their suggestion to raise TA (what you call alk) is crazy

Phosphate remover is their cash cow, a normal suggestion to everyone

My gut tells me that something is starting to grow and is using up the chlorine Rear you add it.

Generally you won't have ammonia if you are registering CYA in the water.

Remove all solid forms of chlorine. Add liquid that should get you to 10FC. Test in 30 minutes with the pump running and see where the FC is.


So, welcome to TFP!!
 

skasyjan

Member
Jun 4, 2020
14
Central Indiana
I may have been updating my original post while you were responding.

I am obsessive, so my tests have been done with the Taylor Test Kit (2006), a ColorQ test kit, Test strips (read manually), and test strips read by smart phone app. (I also have a tester for TDS which I generally use for my interior water, but I have been desperate so broke it out in this process as well.) And they all were about the same.

I generally use Liquid Chlorine, Borax, etc. as my chemicals.
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,976
Franklin, NC
OK, lets stick with the K2006.

The reliability of the ColorQ is still out with the jury, but for maintenance it's generally OK. While fixing a problem, lets just not introduce variables.

Test strips, no matter how you read them are junk and we do not deal with them.

I'm going to guess your CYA test is from the ColorQ, so I'd like to see one done with the K2006.

Let's try my liquid chlorine test. So, not knowing your liquid % here are the amounts depending on the % you have-

327oz 12.5% or

409oa of 10% or

459oz of 8.5% or

665oz of 6%

After adding wait 30 minutes with the pump running and test FC with the K-2006. You can do the CYA with the K-2006 at the same time.
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,976
Franklin, NC
I have the 10% Liquid Chlorine, added about 409 ounces and let circulate for 30 minutes...

Taylor K-2006 FC was like 8.8
The CYA was between 40 and 50 (closer to the 40).
Well, you are holding chlorine. You lost a little.

The next test will be the determining factor. It's what we call an overnight chlorine loss test. Only two things deplete chlorine, UV rays form the sun and something organic in teh water. So, we test overnight to see what happens. Here are the full directions:

 

skasyjan

Member
Jun 4, 2020
14
Central Indiana
As of now (roughly 5 1/2 hours) after last reading. The sun has been hitting the pool all day...

FC 3.6
CC 0.4
PH - 7.4
Alk - 140
CYA - 40-50
CH - 230

Tests done with the Taylor 2006

According to the App, it looks like adding 100 oz to get to FC of 6, 183 oz to get to FC of 8
 

skasyjan

Member
Jun 4, 2020
14
Central Indiana
Last night I added more chlorine to pool. Bumped the FC to 5.6 taken after dark and after circulation for 30 minutes. By calculation it should have bumped it to 6.0... so it seems I continue to lose something “immediately” even with no sun.

I was up late and didn’t get my sample until a 3 hours after sunrise. Pool is getting sun but not quite full direct sun. FC is 3.4...

Even assuming 3 hours of sun, a drop of 2.2 FC seems a lot?

Help. 😄
 

skasyjan

Member
Jun 4, 2020
14
Central Indiana
About 4 hours since last test.... no chemicals added...

FC dropped to 1.2
CC 0.4
PH 7.4
Alk 130
CYA is in the 40-50 range
CH 220

The Non-chlorine results seem to be pretty stable at this point, but in about 16 hours since last night I lost 4.4 FC. At this rate it seems that I would be at 0 by sunset.

Any suggestions are appreciated.
 

djm003

Member
Jun 5, 2020
5
Wisconsin
I would take chlorine up to 7 at dusk and do the overnight loss test but catch it before sun in the morning. I've had sun take out chlorine really fast installed auto cover to help. 2 gallons of 10% should get you there. Add at dusk take reading couple hours later compare to morning result.
 

skasyjan

Member
Jun 4, 2020
14
Central Indiana
Added more chlorine, to bump it up to about FC of 6.0 yesterday evening, when I took my sample last night after it was dark and FC was 5.6... this morning, with no effect of sun it was 2.0... so it dropped 3.6 FC overnight... (I didn't test it at night more than once because it seemed inline with what I was expecting, but this morning's sample was so low I did test the water multiple times and all results were consistent... 5 different water samples, 2 tests each for 10 tests, 8 of them at 2.0, 1 at 1.8, 1 at 2.2)... so I am confident...

Rest of the numbers are essentially the same was yesterday (only tested them once though...)

FC 2.0
CC 0.2
PH 7.2-7.4
Alk 130
CYA is in the 40-50 range (very close to 40)
CH 220

Additional Notes:
- The Pool Water was and is Clear
- Yesterday evening, I did find some algae (I think) around the pool drain on the floor int he deep end. It was impossible to see, even up close, but when I dove in and scrubbed around the fixture it sort of flaked up

So with the presence of algae plus the overnight loss, I believe my answer is to SLAM...

With my other results, I believe my next steps are:
1. Decrease PH to 7.2 (it's hovering around that range right now)
2. Assume CYA at 50 as the higher end number
3. Add Liquid Chlorine to bump it to SLAM target of 20 (I use 10%, so Pool Math is telling me that is 751 ounces (or a little shy of 6 gallons)
4. Let it circulate and then test and maintain it....

Some questions since I have never done this with a pool that was otherwise "clear"....

1. I have an automatic cover, does it make sense to cover the pool to limit chlorine loss to sunlight? (Or leave it open for more air circulation.)
>>> Similar question - the next two days have heavy storms predicted; we cover the pool during storms is this okay?

2. Since my water is clear and the CC is nominal, would it make sense this process would be a shorter process
>>> I have got 18 gallons of chlorine on hand at the moment, so just trying to figure out if I need another run for this or if I can wait until next weekend

ALSO - If I am making the wrong assumptions or missing something please correct me.

Thanks!