CH Test Differences - Mystified

[Beargfr]

First time pool owner here, and I do all my own maintenance, testing, and management. The pool as been 'online' for about 18 months, is about 40,100 gallons, and uses regular chlorine sanitation.
I use a Taylor K-2005C kit, always stored indoors and kept cool. None of my reagents are expired/past their "best by" dates, most have at least 6 months of life left.
I occasionally also take samples to Leslie's, mostly just as added insurance and confirmation, since this is my first ever pool and I want to be sure I'm doing things correctly. Their results using their machine have always been really close to the numbers I get, across the board.

Until today.
We had a tile replaced over the past few days, which meant I had to pull the water down below the tile line, and I took advantage of the opportunity to replace about a 3rd of the water to deal with a CH that had gotten too high. I'd been using calcium hypo granules for chlorine because I didn't know any better. I've now switched to 12.5% liquid for good. My water has always been gorgeous, crystal clear, and I've never gotten a Leslie's score that was less than 90% - most frequently it's been 100%.
Today I tested the water for CH after getting the pool back up to level, pump running for several hours. FC was 2, TC was 2 (I'm going to shock it tonight just because it's been awhile), pH was 7.4, TA was 120, CYA was 50 (it had gotten a little high also). CH using the Taylor kit STILL came in at 410, which bothered me. I needed to go to Leslie's anyway to stock up on 12.5% liquid so I took a sample with me. Their test report matched mine across the board, all except for CH. They reported 280, which was a surprise. I went to another Leslie's across town and had them test - same result as at the first store - all match mine except for a CH of 280. Thinking that even through they weren't expired there might have been some problem with my reagents, I bought a brand new set of the 3 CH test reagents and used them to test a fresh sample when I got back home. Same as before - 410.

So, now I'm struggling with two questions:
Which result do I trust?
Why could there be such a huge difference?

I don't expect to get EXACTLY the same results as they do, but having their measurement come back at nearly HALF of mine is more variance than there should be, I'm thinking.

I hope someone can help me understand what may be going on?

Thanks,
Rob

 

[YippeeSkippy]

Rob, oh Rob.... how can you doubt such a fine test kit as you have in your possession?? Leslie's results are usually 90% wrong!! We only trust your results and hate that you're questioning yourself. You can't trust that they've calibrated their machiines, that the person doing the testing knows the proper procedures, etc. I wouldn't be surprised that your 2nd Leslie's water test wasn't done till after they got your address and looked up your previous results. Calcium doesn't change quickly.

First off.... Do you have a Speed Stir type device?? They make testing soooooo much easier, especially for CH.

Taylor SpeedStir

tftestkits.net

Next I'm going to ask you to run a CH test on your fill water- is it city water, or well water? You may be dealing with hard water. Let us know your result.

You say you were using CalHypo... so you know you were putting a LOT of calcium into the pool. So your drain while working on the tile may have helped but it still is >400. That's not a terrible number, and you can manage it to avoid scale. We'll help you out.

Also, please provide me with these test results from YOUR test kit
FC
CC
pH
TA
CH
CYA
Salt if applicable

Your K-2005C test is missing a VERY important element- the FAS-DPD high level chlorine test for FC and CCs. Order this and you'll be set with the kit we like folks to have- FAS/DPD Chlorine Test Kit

Please go to <Settings> and <Signature> and fill it out with details about your pool- size, equipment in use, how you sanitize, test, ect,. Those details help us answer your questions without asking you a ton of questions repeatedly.

I'll check in to see what you say later on today,

Maddie

 

[Beargfr]

Results from this morning, my kit (remember I shocked it last night and it's still early here)

FC 10
CC 0
pH 7.8
TA 130
CH 400
CYA 50
My kit has the DPD test (Taylor's R001, R002, R003) - Test FC with R001/R002 to get FC, add R003 to get TC - subtract difference to get CC.

I'm on a well. Water here is very hard coming out of the ground, but we have a good softener system in place. The only source for getting un-softened water is at one spigot right at the well head. Everywhere else on the property, the water is softened. I replenished the pool water out of a hose. We have an autofill system but it would have freaked out over how long it was going to take to get the job done, so I had it turned off until the job was done. When I started, and after the hose had run for a few minutes, I tested the water coming out of the hose using my kit. There was no detectable calcium at all. This morning, I ran kitchen faucet for a few minutes and tested that - same result: no detectable calcium. Therefore I feel "pretty good" about the water quality I was putting back into the pool. It's difficult to say accurately how much water I had pulled out of the pool because it's an irregular shape and has a deep end for a diving board, so the bottom is anything but flat. The depth is 3'6" at the shallow and 8' under the board. I had drained it down by about 20" before beginning to replenish. I do have a copy of just the perimeter plan from the builder, not the bottom profile, and I'm in the process of attempting to 'draw' it in FreeCAD so that I can get a better idea of how water level relates to volume, but I don't have that completed yet.

Also this morning, ran the CH test -many- more times and even ran some using the original test kit that came with the pool from the builder. They all got the same result - about 400 CH. I know that's right at the top of the OK range but I'd rather be at the other end of that range, because I figure with the evaporation and other weather/environmentals it's going nowhere but up over time. Considering how long it takes to put water in this thing (the initial fill took over 72 hours with two hoses doing the job running around the clock, replenishing that 20" out of one hose took over 24 hours), I'd prefer to not have to do it often.

I'll head over to the settings link you mentioned and load the rest of the information, but I'm leaning towards thinking that the results I'm getting from my test kit are probably the right ones. Doggone it. While the water was down I took that time to try to address some white deposits that had started to form on the grout between the tiles, and a 'line' across the faces of the tiles themselves. I don't know what that stuff was, but straight muriatic acid out of a spray bottle didn't phase it one bit, even with scrubbing with a coarse grill scrubber pad. I finally ended up using a brass wirebrush wheel in my cordless drill to get it off. That's a job I sure don't want to ever have to do again.

Good thing we're on a well so water is essentially "free", except for the power it takes to run the well pump and the cost of salt to backwash the softener resin beads.

I'll try to insert part of the perimeter plan:



I did just try to add info to my signature but it was rejected for being too long, so I'll include it here:

In-ground, 40,100 gallons according the the builder
Location: Approximately 30 miles west of Fort Worth, Texas
Water Source: On-property well with softener

Pool is 8' in depth under the diving board decreasing to 3'6" depth at the opposite end.
Equipment:
* Jandy VSSHP270AUT E-Pump
* Jandy DEV 48 DE filter
* Jandy JE3000T Heat Pump/Chiller
* Polaris PB45SQ booster pump
* Polaris Black Max 280 - F5B Cleaner
* Levolor autofill
* Jandy K1100 Autofill
* Jandy RS 8 iAquaLink Computer Control
* Jandy BWVL-MPV-80 Multi-Port Valve
* Powerclean Powerclean Ultra Chlorinator
* Taylor K2205C Test Kit

Pool has three (3) sheer descents controlled by a remote enabled valve actuator, 3 LED "multicolor" pool lights, diving board.

 

[Beargfr]

Addendum, I did just now try to add all my pool info to my signature, but it was rejected for being too long. I'm out of time right now - back later

 

[Mdragger88]

Rob,
I suspect u have been maintaining too low of fc levels.
If you keep your fc above minimum for your cya FC/CYA Levels at all times there will be no need to “shock” your pool on a regular basis/schedule or just because “it’s been a while”. If u have algae, cloudy water, or fail an Overnight Chlorine Loss Test you would then do the SLAM Process. But maintaining fc above minimum for your cya generally prevents that need.
Minimum fc for a cya of 50 is 4ppm which is something u don’t want to broach.
You want to aim for the high target on the chart (8ppm) so u don’t play kissy face with minimum ever.
Shock/slam fc level for u is 20ppm.
Your current test kit only goes to 10ppm with accuracy so you can see why the fas/dpd test Maddie mentioned which goes higher than that is necessary incase u need to do the SLAM Process/raise to shock/slam level for some reason.

CYA Chlorine Relationship - Further Reading

www.troublefreepool.com

Also,
Do u have the PoolMath
App? U can Use it to calculate additions & turn on csi tracking to help u manage your csi to protect your surfaces & equipment.

 

[Beargfr]

I've never once had cloudy water or any algae, and I generally keep my FC levels around 5 or more. The only reason they tested at 2 yesterday was because I had just finished replacing what I'm guessing was about 1/4 to 1/3 of the total pool water and had not rebalanced it yet. I've only needed to shock the pool maybe 3 times since last March, and that includes last night. The only time I shock it is when there's any detectable CC, as there was when I checked it yesterday afternoon, and that was less than 1 point, just a barely noticeable color change when I add the R003 DPD reagent, so slight that it was a tossup as to whether it was really there.

My issue is not now nor has it every been lack of sanitation, and I really don't want this thread to go that direction.

That's not the help I need. My only issue is knowing which CH test results to trust, if I can trust any of them.

Cheers,
Rob

 

[Mdragger88]

Bottom line, Trust your results,
They are reliable & repeatable.

I mentioned the fc as it was a red flag being low & this is a teaching forum so I would be remiss to not warn u & just assume you were aware of the need to maintain above minimum for your cya. People come here every day very unaware that their pool is under sanitized or otherwise out of wack because the pool store told them their #’s were great & they always get a high score from Leslie’s.

 

[HermanTX]

If you tested your tap water and got no Calcium and you used that same test kit to test your pool water, that would indicate your test reagents are good. So believe your test on CH.

What I don’t understand is why your CH got so high if you fill your pool with water via the water softener? Did I miss read something?
You did indicate shocking your pool and if you use Cal-Hypo then that would be a source of increasing CH. Stay with liquid chlorine (LC) to raise your FC if needed.

A level of 400ppm on CH is good - now the question is can you maintain that or must you use non-softened water to your pool?
Keeping your FC at a suitable level will avoid the need for shock. I have been using LC for years and never have shocked my pool other than when I added extra LC as I was away for a long weekend and could not add LC daily.

 

[Beargfr]

CH got out of hand for two reasons, the main one being that I didn't know any better and had been using Cal Hypo granules exclusively whenever tests showed some was needed. I've been doing that ever since the pool came online in March of 2021. Now that I know, I'll be using 12.5% liquid exclusively from now on.

The other reason was back last March when the pool was first being filled, our water softener was having issues that had not yet been detected so the initial fill was over 300, as I found out during my "pool school" from the builder when they were teaching me how to run the tests. After that, I found a problem with the softener and fixed it, but it was too late for the pool fill.

The kit(s) the pool builder supplied me were all from Pentair, but I very soon quit using those and got the K2005C and have been using it religiously, usually at least twice a week, more often if I'm making adjustments.

Since last March I've "gotten to know" the pool and can usually predict what it's usually going to need from week to week. I don't test CYA or CH very often, but I do stay on top of FC, pH, and TA. pH likes to creep up and will generally need about a gallon of acid a week (big pool). I like to keep it in the low end of the good range, around 7.2. TA is always at least 80, but I like it higher 90-100. I was a little surprised by the high TA I got from Leslie's but it wasn't very far off from what I'd gotten myself. I'm writing that off to having replaced a bunch of water and am going to wait and see what it does over the next week, especially after I have to add some acid as I suspect I might. With this water volume it takes just shy of 6 pounds of baking soda to raise TA by 10 points. Good thing I've found a relatively inexpensive source to buy it in bulk, because since the pool came online I've already gone through at least 150 pounds of it.

I think the deposits on the tile I removed must have been calcium silicate and not calcium carbonate, because straight muriatic acid out of a spray bottle didn't touch it at all. I read minutes ago just before coming here about that, how hard it is too remove, etc. and that lines up with the experience I had.

I've been "doing what I do" after getting those wildly different CH test results, which is research the snot out of it, and I'm starting to think maybe my test results are the right ones. I hate that because it means if I'm going to get the levels down to where I want them, I'm going to have to replace water again. Oh well, better to do it now than have it bite me later. I don't EVER want to have to deal with those deposits ever again.

 

[Mdragger88]

Do u have a specific reason for trying to keep ta higher? Having a lower Ta (around 60-80) will help moderate ph rise - no need to add baking soda unless it goes below 50ppm. A lower ta will also aid in keeping csi in check which will prevent scaling. Many often find they kind of reach a “happy place” allowing for less frequent acid additions with ta around 60. Between that & now having ch under control things should be less fluctuating .

 

[HermanTX]

CH got out of hand for two reasons, the main one being that I didn't know any better and had been using Cal Hypo granules exclusively whenever tests showed some was needed. I've been doing that ever since the pool came online in March of 2021. Now that I know, I'll be using 12.5% liquid exclusively from now on.

Great.

The other reason was back last March when the pool was first being filled, our water softener was having issues that had not yet been detected so the initial fill was over 300, as I found out during my "pool school" from the builder when they were teaching me how to run the tests. After that, I found a problem with the softener and fixed it, but it was too late for the pool fill.

Thanks for update.

Glad to see you resolve the build up and the lower CH will help.

This is a great forum and most issues can be solved by someone on this forum that has the knowledge or prior experience. Good Luck.

 

[YippeeSkippy]

How low do you want to get your CH??
I put your test results in to PoolMath and the results were concerning. If you drop your pH to 7.4, and your TA to 80 the CSI will look entirely nicer.
Calcium Saturation Index (CSI)

Lower Total Alkalinity

A lower Total Alkalinity level can help a pool owner stabalize their pH increase. We'll explain how to lower TA with a little help from muriatic acid.

www.troublefreepool.com

If you know you're going to get a good drenching rain, drop the pool level an inch or so each time and let the rain refill it. Free, calcium free
water!

The white stuff on your tile & grout is probably Efflorescence - Further Reading

 

[Beargfr]

Do u have a specific reason for trying to keep ta higher? Having a lower Ta (around 60-80) will help moderate ph rise - no need to add baking soda unless it goes below 50ppm. A lower ta will also aid in keeping csi in check which will prevent scaling. Many often find they kind of reach a “happy place” allowing for less frequent acid additions with ta around 60. Between that & now having ch under control things should be less fluctuating .

The only reason I have, is that during a conversation with our construction manager back just after the pool was completed (and I knew almost nothing about keeping it balanced), he told me about how he used to manage very large commercial pools and said that he liked to keep TA high because it kept pH from being so sensitive/variable. At least that's what I THINK he told me.
Other than that, no reason.

He also mentioned that he liked to use CO2 injection because it tended to drive TA and pH in opposite directions from each other, and that sounded good to me too. I've considered going that route here but it hasn't gone beyond that. I've never quite understood how it's possible to have high alkalinity and low pH at the same time because it seems to me that both of them are measurements of the same thing?

 

[Beargfr]

How low do you want to get your CH??

Probably somewhere into the 200's, according to recommended ranges I've seen "all over the place". That's even what the builder recommended.

I put your test results in to PoolMath and the results were concerning. If you drop your pH to 7.4, and your TA to 80 the CSI will look entirely nicer.
Calcium Saturation Index (CSI)

Lower Total Alkalinity

A lower Total Alkalinity level can help a pool owner stabalize their pH increase. We'll explain how to lower TA with a little help from muriatic acid.

www.troublefreepool.com

My test kit has a circular slide rule that will also tell me CSI. I confess I haven't been using it as often as I probably should. I'll change that.

If you know you're going to get a good drenching rain, drop the pool level an inch or so each time and let the rain refill it. Free, calcium free
water!

My water is already mostly free, since we're on a well. Rain has been especially scarce here for months. Up until the 3 inches and change we got last week, everything had been so dry that all the grass had gone dormant since the beginning of summer, there have been wildfires "everywhere", and we've been under a burn ban since long before July 4.

The white stuff on your tile & grout is probably Efflorescence - Further Reading

I doubt that. I followed that link and the next, and got to the "how to remove" part of an article.
It said

In general, most efflorescence can be removed by dry-brushing followed by flushing with clean water.
...
As a last resort, a dilute solution of muriatic acid (5 to 10 percent) is sometimes used to clean the wall.

I sprayed that stuff with straight, undiluted muriatic acid and it just ran off of it, having done nothing at all do it. Scrubbing it with a one of those synthetic 'brillo pad' type grill scrubbers also did noting except make my arm tired. I'm staying with it having been calcium silicate. My further reading says the only ways to deal with that stuff is with either copious amounts of elbow grease or hydroflouric acid.

I appreciate the reply though.

I did manage to get an accurate FreeCad drawing of the pool perimeter last night, and now know the surface area at the water line is 962 square feet. That means a foot of water at the surface is about 7196 gallons and an inch is about 600 gallons. If it really does contain 40,100 gallons of water (the only spec I have), if the current CH level really is at 410, if the water coming out of my hose really is calcium-free, then according to my math, if I want to lower CH by replacing current water with calcium-free water, I can use this relationship.

(inches * 600) = volume of water in one inch of depth
(40,100 - (inches * 600)) = volume of water remaining
((40,100 - (inches * 600)) * currentCH) = "amount" of calcium in water remaining
(((40,100 - (inches * 600)) * currentCH)) / 40,100 = newCH after refilling with calcium-free water

Rearranging all that, if I know a target for newCH I can solve for how many inches of calcium-free replacement water it would take to get there.
Inches = (((newCH * 40,100) / currentCH) - 40,100) / (-600)

I just downloaded the PoolMath app, and now I'm REALLY confused about CH. Every other reference source on the Internet I've seen recommends maintaining CH between 200 and 400. However, the PoolMath app says Recommended 250-650 and Ideal is 350-550 ??? According to PoolMath, right now I'm dead-nuts in the middle of the ideal range. What the blue-eyed twinkle toes is going on here?
I've been using a different site and phone app, poolcalculator.com, up until now. They say 200-400. The treatment book from Taylor that came with my test kit lists three (3) DIFFERENT ranges all in the same dang book: 150-400, 200-400, and 150-250.

I can understand that someone might want to poopoo information from other internet sites, but from Taylor? Why the big difference in recommendations? Can someone please explain??

We spent significant money on this pool last year so I certainly want to keep it perfect, but to do that I've got to have reliable information.

TIA,

Rob

 

[duraleigh]

Experienced pool owners on this forum have managed (successfully) CH from 60 to 1000 ppm. Our experience teaches us that 250 - 650 is all within ranges that are successful.

Certainly, follow whatever range you like but ours is what we would suggest.

 

[mknauss]

My test kit has a circular slide rule that will also tell me CSI.

CSI is only available via PoolMath

What you will get with the circular thing is LSI. See CSI and LSI - Further Reading

 

[Beargfr]

Certainly, follow whatever range you like but ours is what we would suggest.

Well of course it is. After all it comes from your site.

I on the other hand don't have any particular allegiance to any one source or set of sources. I'm not saying that one is any better or more reliable than the other - yet. I'm still pretty new at this and still learning. I have this "personality defect" if you want to see it as such, in that I generally won't take anyone's word for anything based on an "I said so". Things have to make logical sense to me from a reasonably objective standpoint. I'm not a chemist, even though I do have a degree in both math and physics, so I freely admit that I don't understand the mechanics of how all the various chemicals in the water interact with each other. But I'd like to understand. So far, it just doesn't make sense to me how multiple sites and sources can have such differing ideas about what an ideal CH range is.

I'm not saying any particular recommendation is gospel, like I said I don't know enough to say that. But I really would appreciate a logical explanation of how so many different recommendations are possible when it comes to CH levels. Does climate have something to do with it? Location? Normal seasonal temperatures? Sunspots?
I don't know "whatever range I like" is yet. I'm attempting to make an informed and logical decision about that, and looking for help that's more than simply "just do it this way".

Thanks again,
Rob

 

[HermanTX]

I just downloaded the PoolMath app, and now I'm REALLY confused about CH. Every other reference source on the Internet I've seen recommends maintaining CH between 200 and 400. However, the PoolMath app says Recommended 250-650 and Ideal is 350-550 ??? According to PoolMath, right now I'm dead-nuts in the middle of the ideal range. What the blue-eyed twinkle toes is going on here?
I've been using a different site and phone app, poolcalculator.com, up until now. They say 200-400. The treatment book from Taylor that came with my test kit lists three (3) DIFFERENT ranges all in the same dang book: 150-400, 200-400, and 150-250.

This is where the CSI or LSI is important because tap water is so different across the USA. The harmony of CH, pH, TA and CYA is the critical figure I look at when I do my tests which in Pool Math is CSI. I think you referred to the Taylor Wheel which calculates LSI. Also, vinyl and fiberglass pools would have different requirements which may explain some of the differences in the ranges you may find on the internet. In my research I found you definitely want to be above 250ppm with a plaster pool. If you get extremely high CH then you have to manage the other parameters to bring your CSI/LSI value to that zero point to avoid scaling with high CH.

There are some good articles in the WIKI at botTom of page.

 

[Beargfr]

Talking yesterday with my construction manager who ran our project last year, he gave me another ingenious way to lower CH without having to replace water. Use a small self contained water softener with the inlet connected to the hose bib that's already present near the pump, after the filter, on the feed to the returns. Use a "plain old hose" on the outlet side to route softened water back into the pool. Run the softener until the CH level is where ever you want it. With a small self contained unit, like the Rheem RHS32 for example, you can make the whole setup portable. Disconnect the hoses, unplug it, move it around with a 2-wheel dolly. Best of all, you can hook it up, let it run, and still be able to use the pool while it's doing its thing.
He told me about using that solution to deal with a new pool that had a CH starting out at over 1100 and was able to correct it within a couple of weeks time.
This guy managed large commercial pools for years before getting into the construction side of the business and I trust him.

 

[mknauss]

Chlorine destroys the resin media in a water softener. This will not work unless the FC in the pool water is zero.