New Construction: Cathedral City CA

[Dirk]

Digest some of this when you’re ready to. There’s nothing immediate here...

Did you ever test your fill water? What is the CH and TA of your fill water? If either is high, then replacing evaporation with fill water will drive them up. And CH doesn’t evaporate, so it will eventually require a water exchange to control. No sense giving CH rise a head start by adding chemicals if your fill water and plaster will do that anyway. First things first though. When you get a chance, run salt, CH and TA tests on your fill water. Create a new pool in PM and name it “Fill Water” and track your results. Fill water can change over time, so recording tests results in PM is a good way to observe that, for future reference.

When you post results, can you include CSI? Be sure to input your pool’s water temp into PM each time you report results, as water temp affects CSI. Salt, too, to some degree.

We know from before that your targets were influenced by some other Pool Math setting. When you compare your results to targets in the PM calculators, or seek dosing advice, be sure your targets are within the recommended ranges for a non-SWG pool. Midway, as you’re proposing, is logical, but is not necessarily the best strategy long term. Well come back to that before you adjust anything other than FC and pH. Those two are the focus for now.

 

[Yorker]

Morning Dirk,I did test our tap water a month or two before the actual fill. I forgot that I had posted them and since I just recently discovered the "search thread" feature, I was able to locate them.

Tap Water Test
CH Test - 110 to maybe 130
TA - 120
PH - 7.8

I will start a new pool in pMath and track our fill/tap water ... would once a month be sufficient?

I've forgotten to include the CSI and pool temps - Will be better at that.

 

[Dirk]

I think a few times a year for testing fill water is fine. I wouldn't expect it would change all that much, we're really just trying to determine if it does actually change at all. My city's water does, because they switch between ground water and lake water based on availability. I imagine other municipalities provide water that wouldn't change much at all. Just depends on the water source(s). Don't get wrapped up in this, it's going to be what it's going to be, and the pool's water test results are all that ultimately matter. You use fill water measurement for the following, strategy type stuff.

So the CH of your fill water is lower than the recommend level for a pool. Which is good. But that doesn't mean it won't contribute to CH rise, just more slowly. Your pool water will evaporate, but leave all the calcium behind. As the water is replaced with city water, that brings in more calcium, which also won't evaporate. If the incoming water has CH110, that will contribute to the CH rise more slowly than fill water of CH350 (like mine), but either water source will increase CH in a pool over time. How much time depends on how much water is evaporating. I converted my fill water source to soft water, with CH-zero, so I eliminated (mostly) this CH-rise issue. A conversation for another day.

Don't worry about TA for now. I learned here that TA tends to live where it wants to, and only when it's extremely out of range do you take it on. If you chase a number, just for the number's sake, you can end up in a bouncing battle that you won't likely win. So just keep an eye on it for now and see where goes as your pH level stabilizes as your plaster does.

So, leave TA alone.

And we'll check on CH later, when you convert to SWG and the CH range changes dramatically. I'm still learning that part myself, because the two CH ranges (between SWG and non-SWG) are dramatically different. I was told that has to do with manipulating CSI, and CSI is the thing to watch as much as the other levels, when it comes to plaster health and longevity.

So whenever you post pool water results, please include CSI, and we'll keep an eye on that as we go.

 

[Yorker]

Thanks again Dirk!

I have been holding off on this question for a bit, but now seems like a good time to introduce it. I noticed our auto-fill was not working a week or so ago. It turns out they put the backflow valve on backwards. They fixed it, but a couple days later I saw that it still was not working. They discovered there was a bunch of "crud" blocking the flow at the auto fill. It looked like some plaster/pebble mixed with pvc shavings (but who knows). So it's working...

I always hear a slight hiss. I pointed this out the last time the pool plumbing guy was here (10 days ago or so). It was a bit breezy that day and he said that was normal because the wind was causing the level to fluctuate. Made sense. Though, like I said I've checked it at least 5 times when it is fairly calm and I always hear the hiss.

Do you think this is normal?

Another question I have is regarding returns. I believe we have 3, inside the pool and the spa has 4 jets that push water out when the pump is on as well. Two of those jets push a good amount of water out and the other two push out notably less. I do feel water coming out of the three returns inside the pool, but is very gentle.

Is THAT normal when our pump is set to 2500 rpm.

 

[Dirk]

Can you take a picture of the guts of your autofill system?

 

[Yorker]

Here you go...

 

[Dirk]

Inline.

I have been holding off on this question for a bit, but now seems like a good time to introduce it. I noticed our auto-fill was not working a week or so ago. It turns out they put the backflow valve on backwards. They fixed it, but a couple days later I saw that it still was not working. They discovered there was a bunch of "crud" blocking the flow at the auto fill. It looked like some plaster/pebble mixed with pvc shavings (but who knows). So it's working...

Did we cover this? I couldn't find a picture of yours quickly. Your back flow device has a valve down stream of it (the auto fill valve). Which means, while the autofill is not running, the pool-side of the back flow valve is under pressure. If the back flow device is not rated for that, it can (will?) fail at some point. Having it connected the wrong way just increased those odds, because what should have been facing the pool side was under full pressure that whole time, on the "street side." A "lawn sprinkler" type back flow device, can only be under pressure like yours was, and now is, for 12 hours a day max (if I'm remembering all this correctly). So that's step one, to determine which valve you have and if it's the right kind. If it's rated for your application, then you're good. If not, it should be replaced with the correct valve. (Guess what? I cover this in one of my threads!! )

I always hear a slight hiss. I pointed this out the last time the pool plumbing guy was here (10 days ago or so). It was a bit breezy that day and he said that was normal because the wind was causing the level to fluctuate. Made sense. Though, like I said I've checked it at least 5 times when it is fairly calm and I always hear the hiss.

Do you think this is normal?


Could be, but it's something to check. The hiss could mean any of a few things:

1. You've just happened to catch it, every time, filling your pool. If you have a lot of evaporation, and/or that reversed back flow valve was not providing enough flow to fill your pool fast enough, then it might run a lot of the time, even most of the time.

2. Your pool has a leak, and the autofill is running constantly (or a lot) to maintain water level.

3. The autofill valve has crud in it and can't seat properly to seal when closed. If that, then your pool would be overfilled and water would be dumping into your overflow outlet (which I was hoping to see in the pic, but your autofill is different than mine, so I can't tell either way). Do you know where your overflow pipe starts (either in the autofill housing, or somewhere along the side of your pool)? Is water draining into it while the autofill valve is hissing?

Keep in mind, that the auto fill could be failing (and hissing), then some event appears to fix it (like cleaning, jiggling it, the pool filling and moving the lever, etc). And then the pool water drops and the thing goes back into failure mode, at some later date. I'm right in the middle of this very thing. I fiddled with my autofill water source, probably got dirt in the pipe upstream of my autofill valve, so the valve got stuck open. I cleaned and fixed that, promptly forgot about it, only to find it "hissing" non stop one day, a few months later. Turned it off for a while. Turned it back on and now it's working again. Intermittent! The worst kind of failure. For $25 I'm going to replace the entire unit and stop fudging around with it.

I think that's all (most?) of the possibilities. Maybe somebody else has another idea, but those are three you can troubleshoot first. If it's intermittent, replace it.


Another question I have is regarding returns. I believe we have 3, inside the pool and the spa has 4 jets that push water out when the pump is on as well. Two of those jets push a good amount of water out and the other two push out notably less. I do feel water coming out of the three returns inside the pool, but is very gentle.

This is why it's advisable to have all of a pool's returns on their own valve back at the pad, so each can be dialed in and balanced with the others. Are yours plumbed that way? That's a lot of pipe, and a lot of valves, and so that very nice feature is often skipped over for budget concern. Each return has a different length of pipe running to it, through a different amount of elbows. They're virtually guaranteed to output a different amount of water. Mine do that, but I don't have independent valves, so I got what I got. With your setup, you'll have some number of valves that direct flow between pool and spa, so I'd expect some amount of balancing could be adjusted using those. You'd have to review with the PB, which valves do what, which returns can be individually controlled, if any. Short of that, I read somewhere that you can try different sized eyeballs to regulate flow. Haven't tried that, so I don't know how well that would work, or if that's even a real thing.


Is THAT normal when our pump is set to 2500 rpm.

I'd expect that while RPM might affect to some degree the amount coming from any one return relative to another, it couldn't eliminate the issue altogether. So if return A was pushing less wear than return B, turning up the pump might make that relative difference a little more, or a little less, but there'd still be a relative difference. That's just a guess, though. That, too, is easy enough to test. But you have to understand all your valves first. Until you do, you won't know if this is an actual trait of your plumbing, that you'll have to live with, or just something that needs a tweak of a valve to correct.

 

[Yorker]

Morning Dirk!

So that's step one, to determine which valve you have and if it's the right kind. If it's rated for your application, then you're good. If not, it should be replaced with the correct valve.

Yes, we did discuss valves and if I recall correctly you recommended Flo-Vis. I know I mentioned this to the PB, who had no idea what I was referring to. He said they use what the city requires. There was other things that seemed more pressing at the time and just went with that.

Here is a photo of ours in it current state:
View attachment 75596


3. ... Do you know where your overflow pipe starts (either in the autofill housing, or somewhere along the side of your pool)? Is water draining into it while the autofill valve is hissing?

Not sure what/where to look for the overflow pipe. Any hints?

 

[Dirk]

The FlowVis is a flow meter, for measuring the amount of flow through your pool's PVC plumbing (pump, filter, SWG, etc) and that's not related at all to your back flow valve on your autofill system.

I can't view that attachment. And I'm not a back flow valve specialist, by any means, I know what I know about them from a friend who absolutely is. You've seen that little gizmo that is part of a sprinkler valve, right? It has a cap on it, about 1.5" round or so. That is a type of back flow preventer. It's suitable for that use because once the sprinkler valve shuts off, the water drains from the sprinklers, and the pressure pushing on that back flow preventer component is relieved. So, in essence, it gets a rest. Those types of BF devices are rated to withstand that pressure for a max of only 12 hrs, and must have their "12 hrs of rest." If you put a valve down stream of that, say, instead of a sprinkler, and that downstream valve is closed when the BF valve closes, then the water doesn't drain, the pressure remains and the BF's "rest period" is compromised, which can lead to its failure.

From what I remember about your autofill's BF valve, is that it looked a lot like a sprinkler valve. And because the autofill valve is downstream of it, and the BF valve is always open, then that BF component could be under pressure for more than 12 hrs at a time. Certainly will be during the colder months, when the water isn't evaporating and the autofill valve could remain closed for days or weeks at a time. So what's the big deal? If I'm remembering your valve right, it is the type that has no testing ports. So it can't be tested. So if (when?) the BF prevention fails, you won't know it, won't be able to test for it, and it becomes just a faucet at that point, with no BF protection.

If your valve is not rated for that use, the fact that the city approves that, or that maybe the PB and/or the inspector don't understand that, is one thing. What you want on your system is another, and for you to decide. I'm only offering something for you to consider and follow up on if you choose. Technically, you did all you had to do to be compliant, but that doesn't necessarily mean that you actually have a viable back flow preventer where one should be. The fact that they put the thing on backwards speaks for itself...

Your PB would know where the overflow drain begins and ends, if there is one. Mine is inside the housing for the autofill. Others can be just a hole in the tile under the coping. Some of those have a grate in front of them. There could be other types, too, I suppose.

 

[Rancho Cost-a-Lotta]

My pool is a couple years old now. I had a similar problem with the regulator between the fill valve and the shut-off valve. My fill valve is connected directly to my sprinkler system which is not controlled by the home's pressure regulator. My water pressure to the fill system shut off valve is about 180 psi. The regulator that was installed by the PB was one of those cheap plastic parts and it failed after the first year causing my fill valve (the toilet valve looking part) to fail. The PB installed a heavy duty brass regulator which solved the problem.

Yorker...I'm not sure if you have a similar set-up, but you should find an auto-fill shutoff valve near your pool equipment. The regulator should be downstream of that valve. It may look like a plastic sprinkler valve as Dirk described, or a may be a heavy duty brass valve. If you have full pressure to your auto-fill system and a cheap plastic part, that is likely your problem.

I try not stick my nose where it doesn't belong, but I had a similar experience.

Hope this helps,

Mike.

 

[Rancho Cost-a-Lotta]

I went back and looked at your valve in Post #199. I have similar shut off valve. Your's does not appear to be regulated as mine is. If you take a close look at the right side of my equipment pad you will see the shut off valve and regulator just below it.

 

[Dirk]

So just to clarify for the OP: a pressure regulator and a back flow preventer are two different things, solving for, and protecting from, two different problems. Either can be plastic or brass, and I'd want mine to be brass, for sure.

The pressure regulator allows you to dial in the amount of water pressure downstream of it.

The back flow preventer stops water from running backwards from the pool into your drinking water supply.

It is pretty common for irrigation to be fed "pre-regulator." I think that could be said of auto-fillers, too. Mine was that way. It's now on the "regulated side" since I connected it to my indoor water softener.

Rancho Cost-a-Lotta, thanks for the heads up, I think it's very possible for too much pressure to compromise the auto-fill valve. That's could be another thing for the OP to check.

Mine is plastic, and while it is normally connected to my softener, I left a way to route "street water" to it, which is still pre-regulator, so I should check on that, too.

- - - Updated - - -

Rancho Cost-a-Lotta, yours is a little hard to make out, but appears to be similar to the OPs, so might be subject to the same issue. If it's not rated for non-stop use, it's not really the right thing to have in front of another valve. It'll turn the water on and off just fine, but it could eventually stop being a back flow preventer, and you won't really know when that happens...

 

[Rancho Cost-a-Lotta]

Thanks Dirk for the clarification and heads-up. I'll try to get the model # and do some checking.

 

[MinerJason]

3. ... Do you know where your overflow pipe starts (either in the autofill housing, or somewhere along the side of your pool)? Is water draining into it while the autofill valve is hissing?

Not sure what/where to look for the overflow pipe. Any hints?

It may or may not be plumbed, and there may be another one elsewhere, but the hole in your autofill pot (to the left of the float in your picture) is designed to be used as an overflow. You should be able to stick something in that hole to see if it's been plugged/capped or if it's plumbed for overflow.

The water level is well below that overflow hole, so it's unlikely that your pool is being overfilled.

 

[Yorker]

Hello All, been MIA with the completion of the pavers, irrigation system being restored, and house guests.... sorry for my delayed response.

First, thanks to Mike and Jason for joining in (and ongoing thanks to Mr. Dirk!) your input.

I't seems that perhaps the photo I posted for the backflow may have not been visible to everyone, so I will post it here again.

From Jason's prompt as to where to look, I did locate a hole to the left of my autofill float. I stuck my finger in and it hits a white colored dead end.

For the sake of "hopeful" clarification, the order of these elements are pool autofill, Shut-off valve / Backflow Preventer, Another Shutoff Valve near the main that comes to the house, then a Pressure regulator.

I now recall questioning why the pipe to the pool's autofill was line was before the pressure regulator (considering we have VERY high pressure in our neighborhood). Their plumbing guy said that that he no longer tampers with the houses pressure regulators because the city made some issue with that.

I'm now questioning if my hissing is caused from too high of water pressure. Our current water pressure is 80 (after the pressure regulator).

PS - when you're referring to OP in the above posts ... what/who is that?

York

 

[Dirk]

OP is you (Original Poster).

From Jason's prompt as to where to look, I did locate a hole to the left of my autofill float. I stuck my finger in and it hits a white colored dead end.

Hmm, so either there is another one somewhere else, or the PB decided not to hook it up, or neglected to. I can't imagine why he wouldn't have used that one, though, if he intended to have one. Perhaps in your area it never rains enough to need an overflow? See if it's handled in some other way. (Personally, I'd want it hooked up, for a freak rain or whatever.) A mystery easily solved by asking the PB.

Back to the original issue, we're trying to see if the pool is at overflow level (based on if the pool water is running into the overflow pipe). If the autofill's float is adjusted such that it is not shutting off the valve when the water level is below the point the pool would drain into the overflow, then it would be running (hissing) non-stop. If you have no overflow, then a mis-adjusted autofill float is not the cause of the hissing problem.

For the sake of "hopeful" clarification, the order of these elements are pool autofill, Shut-off valve / Backflow Preventer, Another Shutoff Valve near the main that comes to the house, then a Pressure regulator.

That's not quite right. The pressure regulator is not part of the autofill path. It goes: un-valved water main -> auto fill shut valve #1 (PVC) -> auto fill shut valve #2 (brass, part of the BF valve) -> back flow preventer (brass, part of the BF valve) -> autofill valve -> pool.

I now recall questioning why the pipe to the pool's autofill was line was before the pressure regulator (considering we have VERY high pressure in our neighborhood). Their plumbing guy said that that he no longer tampers with the houses pressure regulators because the city made some issue with that.

If the pipe closest to the corner is your water main (coming from the city's water meter), then that is a strange choice the plumber made. I have no idea what he means by "tampers with the houses pressure regulators." Whatever. You've got the autofill running off the high-pressure side of the regulator. You've got the sprinklers running off the regulated (lower) pressure. They both have a shut off valve. You've got two shutoff valves for the autofill (that p-o-junk PVC ball valve, and the valve on the back flow preventer). Yikes. Maybe that's all local code, but not at all how I would have done it. And by the way, I'll wager, ummmm, oh, about $20 (the extra profit the plumber made for being lazy), that he tapped that autofill where he did because it would have been easier than doing so after the regulator. And then generated his "contractor-speak" to get you to shut up about it. Obviously, I can't say that for sure, who knows what a city says about what, but it's a little far fetched that any part of a house's plumbing can't be reconfigured/replaced/repaired when there is a need to do so. Regulators need replacing every so-many years, what does the city have to say about that? I'm callin' bs.

My house is plumbed with both irrigation and autofill before the main shutoff valve. (Well, it used to be, before the whole softener mod, but I digress.) The upside of doing it that way, is that I can shut off the house while away (to protect against interior flood damage from, say, a broken washing machine hose), but still provide water to the plants and the pool. The downside is if any components of the autofill or irrigation systems can't handle the max pressure from the street. Trade offs.

A quick fix for your system would be to cap off the T on that main line, delete the ball valve, and use an elbow and a tee and a coupler to tap your auto fill line off the irrigation line (which looks to be all PVC). That'll put the regulator before the autofill. The downside, is that if you had to shut down irrigation for some reason, you'd also be shutting down the autofill. With a little extra effort, the irrigation shutoff valve could be move after the where the autofill taps in. If plumbed either way, shutting down the main valve would also shut down the autofill and irrigation, which could be considered either a pro or a con.

And as long as we're at it, it's interesting that the plumber was so concerned about what the city had to say about messing with the regulator, but was OK with leaving PVC exposed to the sun, which is not OK.

I'm now questioning if my hissing is caused from too high of water pressure. Our current water pressure is 80 (after the pressure regulator).

Well, you could replumb as described above and eliminate that troubleshooting branch.

 

[Yorker]

Good to know that I’m the OP

Dirk: … I can’t imagine why he wouldn’t have used that one, though, if he intended to have one. Perhaps in your area it never rains enough to need an overflow? See if it's handled in some other way. (Personally, I'd want it hooked up, for a freak rain or whatever.) A mystery easily solved by asking the PB….

I’ll ask the PB. I now we get very, very little rain here, BUT I would imagine that there are a day or two maybe every year that we could get very heavy rain. When that would happen, I assume the pool would overflow into … the yard.

IF the PB had installed an overflow (either in the autofill or somewhere else), where WOULD IT HAVE been “hooked up” to … a pipe that drains to the street? I know that was never brought up as an option by the PB (or within my thought process). Time will tell what the outcome of that would be.

I attached the wrong backflow photo earlier - that one was the BEFORE they changed it. The current configuration is in my new diagram below.

Dirk: If the autofill's float is adjusted such that it is not shutting off the valve when the water level is below the point the pool would drain into the overflow, then it would be running (hissing) non-stop. …

The water level of the pool has remained the consistent (halfway up the waterline tile) since the autofill was turned on), so the water level in the autofill never gets close to the level of the plugged hole inside the autofill. IF it ever did get high enough to reach the overflow, the pool’s water level would be at the bottom of the coping.

Dirk: If you have no overflow, then a mis-adjusted autofill float is not the cause of the hissing problem.

IS NOT… the cause?

Here is a butchered Photoshop image with what I believe is the configuration you propose. This is something I could propose to the PB. Not sure what he will say about that.

Bottom line the hissing is sign of some issue.

I’m not sure if anyone has made any adjustments to the autofill's float yet. Maybe that will stop the hissing.

Or maybe the hiss is because the pressure is too high from the street. Not sure if there is an easy way to measure that pressure, or even if a high pressure is the cause. Without the re plumb.

Or could it be a leak in the pool? Yikes!

 

[Yorker]

Chemistry Update:

It took some time for the FC to come down since the Pool Guys visit 5 days ago. Since yesterday I have been able to keep it at 6.0.Before he came yesterday, I added the chlorine and asked him not to add any more, that I would add whatever was needed to keep it 6.0 everyday, he said fine. He also said that his “boss” wanted him to add a lot of MA at one of the deep end where the worse stains are. He did comment that they usually don’t put it near the skimmer, so he was gong to pour it about 6 to 9 feet away. He said this should help loosen sand that was causing the stain.

I did my regular brushing today and saw no difference.

This morning the pH was 6.3. Here are my numbers on the tests I did his evening at 5pm

FC: 5.0
pH: 6.2
CSI: -0.66
Temp: 75

 

[Dirk]

RE: your proposed manifold for valving house, irrigation, and autofill? Perfect. Well, except for the PVC. If you had photoshopped the PVC as if painted, I would have been even more impressed!

You won't have the option to shut off the house and leave water on for irrigation and pool, as I mentioned, but you will have regulated pressure for everything. If you're street pressure is really high, then what you drew is the way to go.

If you want to "dirk" it, instead of removing or plugging the T before the main shutoff valve, I'd be tempted to put a hose bib there. I did something similar. My regulator reduces the pressure quite a bit, so I installed a hose bib "pre-regulator" so I could have "full power" for spraying down sidewalks and whatnot. Not politically correct in these times of water rationing, but sometimes I just gotta go full blast!


If your PB didn't discuss where to overflow your pool, and the overflow port of the autofill pot is plugged, those are pretty good indicators that your pool has no overflow system in place. And yes, if it ever does overflow, it'll run into your garden. Not ideal with a salt pool, but fresh water does float, so theoretically most of the run off will be rain water. Of course, if your pump is circulating while its raining, all bets are off. And maybe why he didn't connect it, or offer to, was because your yard has no ideal place to run it to. It'd have to go to the street or the sewer, and your city might not allow either.


If the water level of the pool has remained consistent, and the autofill is running a lot or all the time, and the pool is not overflowing, then I think it's only one of two things:

1. The pool is leaking and the autofill must run most of the time to keep up.

2. The water is just evaporating and the autofill must run most of the time to keep up.

Either way, it's possible you just haven't noticed yet when it isn't running. I'd guess that if it ever does fill the pool enough, it'd be in the middle of the night some time.

So... troubleshooting steps:

1. Confirm there is no overflow.

2. Go out to the pool as early as you can, and see if the autofill is running. If not, that would suggest it made up for the previous day's water loss at some point in the night, and is shut off until the pool starts to lose water again.

3. Do a leak test.

If there's no overflow, and there's no leak, then I'd have to guess your autofill system is just barely keeping up with evaporation, and there's nothing else actually wrong. The fix? Hmm, not sure. Cover the pool to minimize evaporation? See if you can increase the flow through the autofill system? Different valve? Not sure. Or just live with it. As long as the autofill can keep the pool at the correct level, then all is well, even if it runs 23.99999 hours a day. You'll only have a real problem if evaporation outpaces the autofill, because then your level will drop. And that's bad for a couple reasons. And unfortunately, if it is evaporation and the autofill is struggling to keep up, that's only going to get worse come summer.

Just FYI, 'cause I think we're past this, but let me see if I can describe this better: if there is no overflow, and no other problem, then it wouldn't matter at what water level the autofill valve shut off. If its float was adjusted correctly, then the water level would be mid skimmer. Otherwise the autofill would shut off when the pool was either too high, or too low, but it would shut off. But if there is an overflow, and the autofill's float was not adjusted correctly, then as the autofill put water into the pool, the water level would rise, and keep rising, until the water was running into the overflow system. At that point the water wouldn't get any higher in the pool, and wouldn't get any higher in the autofill pot, but the water wouldn't be high enough to raise the float enough to shut off the autofill valve. So it would just keep running (hissing) and the water would just keep pouring into the overflow system. Endlessly. That's why I have you searching for the overflow system. Because if there is none, then this particular problem would not exist, and so wouldn't be the cause, "IS NOT… the cause", of the hissing.

Further (this is just now coming to me since you wrote the level has been consistent), if there is no overflow, then it is not likely a problem with the auto fill valve, and not likely a problem with the pressure, because if that valve couldn't close for some reason, then your water level would not be stable, it'd be getting higher and higher.

The fact that you said the water level is being maintained at a constant level points back to water leaving the pool at a rate that the autofill is just barely maintaining (so, a leak, or evaporation).

The other possibility, is that the system is fine, but active due to evaporation, and that it runs maybe a lot, but not actually all the time, and you've just happened to check on it when it's running, like it's supposed to. So you'll get one of these:

 

[Dirk]

Part of the problem, and why my posts keep getting longer and longer, is that we're dealing now with three separate issues, mostly unrelated: why the autofill seems to run all the time, whether you have a proper back flow preventer, and how your various water systems are plumbed and valved at the source.

We should probably deal with these one at a time, or this will just continue to get more and more confusing, at least for me anyway...