Testing confusion TF-100 vs pool stores

Elemental21

Member
Jun 2, 2020
12
Buffalo ny
I've had my in-ground 21,000 gallon pool for a year, but just this season started following the TFP method. I have a SWG and have had trouble keeping the FC levels up. That's hopefully going to get resolved by the pool manufacturer, but he wanted me to get a store test to verify there weren't any issues with Phosphates first, which I knew there weren't.

I expected that the results from the pool store would be pretty close to my test results but I was surprised. My TF-100 results are:
FC - 3.5
TC - 4
pH - 7.5
TA - 100
CH - 100
CYA - 60
Salt - 2800

This is what Leslie's test said on the same day and sampled same time as above test:
FC - 2.19
TC - 2.44
pH - 7.6
TA - 70* (adjusted due to the effect of CYA)
CH - 81
CYA - 90
Salt - 2242

So I kinda figured their results might be off. So I went to another pool store that uses "BioGuard" testing. This water test was taken from the pool maybe a hour after the first
FC - 1.7
TC - 2.1
pH - 7.6
TA - 79
CH - 71
CYA - 82
Salt - 2203

So I'm legitimately confused now. I guess FC is not that far off with the Leslie test and maybe it dropped a bit due to the sun in the time I was out getting the first test. I don't know, still seems like a pretty big delta. The CYA almost made me cry. I try so hard to get that test right. I make my wife come over and give me her opinion. I'm shaking that thing for the thirty seconds...etc etc. Also it seems like I get it to 70 and then 2-3 weeks later I can definitely see the dot at 70. TA seems off but Leslie's says they "adjust" it but they don't list the original. The other one doesn't say adjusted so I dunno what's up. The Salt is possibly the one I'm most disappointed about if it's the K-1766 that's off. I spent an extra $30 on that test and it's off by 600 ppm? Is that right? That takes it well out of the ideal range of salt for my SWG. It also could be the reason I've been fighting to keep my SWG making enough chlorine this whole season.

Thoughts on the discrepancies here? Is this just normal variances and I just need to expect this or something else?
 

Teald024

TFP Guide
Hello and Welcome to TFP!!
I would believe your testing over the pool store's results.
You say you are having a trouble keeping FC levels up. What SWG do you have? What % is it set on and how long do you run the pump each day? What does the water look like. Can you post a picture, include the brush in the deep end.

Please fill out your signature with your pool and equipment information. It will help us help you.
 

Mike1162

Silver Supporter
Jun 13, 2015
720
N Tonawanda, NY
Wouldn't the SWG give you a message or fault if the salt level is low?
Do you have the SpeedStir? I'm in N Tonawanda if you want to try one.
You can use liquid chlorine to boost the FC level then see if the SWG can maintain it.
 

Elemental21

Member
Jun 2, 2020
12
Buffalo ny
Thanks for the welcome guys and for the quick response! I will trust my tests.

I added the SWG to my signature. As I mentioned, I've been struggling with it all season long. I don't believe I struggled last season however that was my first season and all I had was test strips so it's hard to say for sure. I was also running the pump for 12 hours last year. Fortunately, despite my trouble with chlorine, I've been a nut about testing pretty much everyday so I've never let the chlorine get too low. There's always been an excuse for the lower chlorine most times involving low flow from cottonwood, other plant stuff in the SWG mesh filter cup, a bad o-ring one time, hair in the impeller, etc. I've learned to really pay close attention to my pressure and what I expect it to be. It really been a pain all season and far more "fragile" than I thought it would be, but figured maybe that's just the reality of SWGs.

Anyway, all season and up until about a week ago I had it set to run 8 hours a day and even though I had to set it at 80-90% it was mostly keeping up. I believe the TFP app says 75% should be sufficient for 8 hours a day so I didn't think that was too bad. Then last week my chlorine was down to maybe 1ppm so I put it up to 100% and it wasn't moving much, maybe 1.5ppm. So I set it to run for 12 hours at 100%. Well it continued to stay low, maybe 2.5ppm - 3.5ppm was about it at the end of the pump runtime. There was no sign that I was going back to 8 hour runtimes. The last couple days I've been supplementing with bleach to keep the chlorine in a reasonable place. A couple days ago I figured I'd try the overnight test to see if something was stealing my chlorine. I added bleach to get it up to 3.5ppm and only dropped to 2.5ppm by the morning. I tried all the suggestions in the SWG manual which mostly involved flushing the system to clear any blockages. I even called the manufacturer of my SWG to see if they had any suggestions. They said the amps were perfect so it should be doing just fine and told me to check my phosphate level. I told the folks who put in my pool about the issue and the service manager said I needed a pool store test to see if my phosphates were high. My phosphates were 0. I added about 160lbs of salt which brings me up to 3200 ppm as per my test. The increased salt had 0 impact on the amount of chlorine being generated.

At this point my guess is that there is a problem with the SWG. Very frustrating.

I will try and get a pic of the vac for you tomorrow if the weather is decent. The water looks fantastic in my opinion.
 

Elemental21

Member
Jun 2, 2020
12
Buffalo ny
Mike1162, in theory yes it should give you a warning that it's low on salt but as I understand it has to be calibrated right (+/- percentage). I adjusted it to be in tune with my test (2800ppm) and then I got the two store tests saying it was more in the 2200ppm range so it was certainly in the realm of possibility, to me at least, that the installers just didn't calibrate it properly and that's why I wasn't getting a warning.

I don't have the speedstir. They were out when I ordered my test. I'm considering picking one up next time I order refills though. Thank you very much for the offer, that's very cool. I don't THINK I could be screwing up the FC test that much especially since I've done 2-3 a day since this debacle started and they pretty much all in order. Plus I have gotten readings in the 6ppm range earlier in the season so I know the SWG was able to get there before.
 

SouthVirginiaPool

Silver Supporter
Apr 26, 2020
104
Chesapeake, Virginia
Have you cleaned your SWG cell since you got it a year ago? I'm not familiar with your brand. I have a Hayward T-15 and I was told to check it every 3 months. You could get buildup on your plates that can affect your SWG production. I would trust your results over the pool store any day. If you have read other posts on this forum there are many reasons not to trust what the pool store employees tell you to do: poor training, not understanding how important CYA ratios are, shooting from the hip and jumping to the quickest diagnosis to sell you a fix ... the list goes on and on. I'm still learning my pool - first year ownership but the advice here from the mentors has been spot on and consistent.
 

Flying Tivo

Well-known member
Jan 24, 2017
1,889
Monterrey, NL, Mexico
Your cell produces 1.52 lbs/day of chlorine gas. This means you need to run 11 [email protected]% to produce 4ppm of FC. Most pools need 2-4 ppm of FC per day. So last year you were very close to that. I would recommend to do a SLAM Process to see if you can get that overnight loss to less than 1. Then get back to running 11-12 hrs a day at 100% and go from there. Cells either work or not.
 

Elemental21

Member
Jun 2, 2020
12
Buffalo ny
What you are describing about last year vs this year definitely not the situation Flying Tivo. This season has been challenging at 8 hours a day, but it has been keeping up when I make sure the flow is ok. At times I've even had to back it down because the ppm reached 6. That may be an indication that it's somewhat undersized but that's not the situation I'm dealing with now. Whatever is happening now it is NOT keeping up at 12 hours a day at 100% and this was a dramatic change, not gradual. As I mentioned, everyday for the last 2-3 days I've had to add additional chlorine to keep it at 3ppm.
 
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Elemental21

Member
Jun 2, 2020
12
Buffalo ny
Mike1162, yes, overnight loss was 1ppm which apparently is OK although that's the outer threshold of OK. Maybe I'll do a SLAM as Flying Tivo suggested and see if it helps.
 

cowboycasey

Gold Supporter
LifeTime Supporter
TFP Guide
Jul 3, 2013
4,113
Fletcher, OK
sounds like a good old SLAM for a couple days and see if you pass the OCLT and run 12 hours a day on 100%... I keep my FC between 5 and 8 when my pump and SWG shut off, mostly like to keep it at 7 and not worry about it.. It is on the high side but that is why I bought a SWG to run it and not worry about the level :)
 

Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,332
Central California
As others have said, ignore the pool store tests. Give the results to the PB for his own satisfaction, but that's it. Just so you're clear: an SWG can't be expected to raise the level of FC. Only maintain it. You bring your FC to level with liquid, then adjust the SWG to maintain that level. You may have to do that for many days, increasing or decreasing the % and runtime, until your SWG holds the level. If it cannot, at a % and runtime that is reasonable (based on its spec for producing chlorine), then you either have something in the water eating up the chlorine (including extra heat/sunshine) or the cell is not working. Sounds like you troubleshot the cell well, so it could be defective. I don't know your brand, or how it calibrates. Mine does not. For mine, the amount of salt isn't a sliding scale, where more or less salt affects production. Once there's enough salt the cell will produce all it's going to: it either will or it won't. It has a salt sensor, and if it's not satisfied it just shuts down the cell, not make a little less.

Once you eliminate any issues with the cell (salt level, cleaning, clogging, flow, etc), and then eliminate any chlorine-eating-issue in the water, that pretty much points to a bad cell (it happens).
 
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Dirk

Gold Supporter
TFP Guide
Nov 12, 2017
6,332
Central California
Oh, another tip. SWGs off-gas hydrogen as a byproduct. In my pool I can see the little bubbles exit the returns. Yours should be doing the same, though I suppose for some plumbing layouts the bubbles might not make it all the way to the pool, so it's not a sure thing. I use the bubbles to double check that my cell is producing. If you see bubbles, that means, at least, that electricity is getting to the cell's plates.
 
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SouthVirginiaPool

Silver Supporter
Apr 26, 2020
104
Chesapeake, Virginia
Oh, another tip. SWGs off-gas hydrogen as a byproduct. In my pool I can see the little bubbles exit the returns. Yours should be doing the same, though I suppose for some plumbing layouts the bubbles might not make it all the way to the pool, so it's not a sure thing. I use the bubbles to double check that my cell is producing. If you see bubbles, that means, at least, that electricity is getting to the cell's plates.
I finally figures that one out myself just yesterday. I had noted fine bubbles coming from my returns. I though maybe I had a small leak somewhere, or air way getting into the pump somehow, or vortex in the skimmer. But the rains filled my pool to the tip top and I still had bubbles. Checked my pump and no air in the filter basket - then I remembered the hydrogen gas production and why running a SWG with no flow can cause explosions - duh. At least I don't have a leak to fix :eek:)
 

Elemental21

Member
Jun 2, 2020
12
Buffalo ny
Ok, the pool guy came today. He took the cell out and capped the bottom of it to make a cup out of it, filled it with my pool water and ran the system for 30 seconds or so. We watched it fizz and bubble and the test strip definitely came out dark purple. I should have tested the water myself but forgot. So I suppose a SLAM might fix this? The only other possible thing I can think is that somehow the water isn't going through the manifold as quickly as it should so it's not making as much as it was. I'll follow up after I get a chance to SLAM.

@Mdragger88 A while back I found a small amount of algae hiding in my bottom drain under the cover. I scrubbed it away and of course did the overnight test so I thought I was ok at 1ppm loss.

@Dirk I just tried it. When I let the blower hit my hand I can see really small bubbles float up but looking at the blower I can't even tell it's on unless I reach in and feel that it's on.
 

Flying Tivo

Well-known member
Jan 24, 2017
1,889
Monterrey, NL, Mexico
The only other possible thing I can think is that somehow the water isn't going through the manifold as quickly as it should so it's not making as much as it was.
That is not the way this works as you witnessed with the Pool guy, the water could be standing and still produce FC. The cell is working! You have something consuming it, either organics or UV. Recheck CYA levers and or SLAM.
 
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