I responded to Steve (medvampire) but just now noticed that CarlD and David (DavidD) had posted, so I'll respond to those posts now. Some of this may be repetitive, but if so I'll try to phrase things differently to make things clearer.

First of all, I believe Carl's summary of how close we are or what we are debating is right-on. So there's hope that I'm being clear about at least a few things as I worry that my jumping back and forth between being very technical and trying to speak non-technically may not be successful.

BTW, Richard's analyses of various reactions has been fascinating. There has long been the comment from bleach users that pH does NOT seem to rise for most of us, despite bleach's pH of 11. Richard successfully explained that the breakdown of the chlorine lowers pH in nearly the exact amount that bleach raises it, creating a balance and sum of a neutral effect. Combined with the proper buffering of Tot Alk, we don't see pH move from adding bleach.

This further explains why I have long noted that di-chlor powder drops pH despite being near-neutral (I believe it's 6.9 in pH). The chlorine breakdown lowers pH and the di-chlor isn't alkaline enough to offset it.
Though the chemistry explains a near-neutral net effect for bleach and a slow net rise from the extra base in liquid chlorine, as well as the net decrease in pH when using di-chlor, the fact is that there are quite a few users out there (see rising ph levels) who are experiencing quite substantial pH drifts upward using only bleach. Some have alkalinity drops (after adding acid to restore pH) and are at least partly explained by outgassing of CO2, but others have no such drop nor explanation. This is a perfect example of where reality does not match the science and yet I'm going to try, with the help of these users, to figure out what's going on if possible. If we fail, then we will not throw out the science of what is explained, but will at least have some parameters for how bad it can fail to predict and in which direction.

Sounds like about half (completely speculative) of the pools out there using trichlor to chlorinate and soda ash to adjust PH. Most people like the "ripple effect" of their returns so there is the aeration right? Also, diving, jumping and splashing around also is considered aeration is it not? Would these all not cause a regular rise of PH?
The use of trichlor is acidic plus the using up of chlorine is acidic so the combination is very acidic. This ends up lowering the pH and alkalinity a lot which is why you constantly have to add some sort of base (soda ash of caustic soda). If you add soda ash, then you are increasing both pH and alkalinity, the latter beyond that which would be increased by pH alone (that is, you are actually adding carbonate to your water). So such users do not see a rise in pH even though they are probably outgassing lots of CO2 because the acidic process (lowering of pH) from trichlor vastly overwhelms the CO2 outgassing effect and its relatively smaller rise in pH.

As has been pointed out, we really have no way of easily and accurately knowing how much outgassing of CO2 is occurring except by witnessing "after the fact" how much the alkalinity drops over time (after adding acid to restore pH). The rate of aeration is not only hard to calculate except from such long-term "after-the-fact" analysis, but it changes in the short-term depending on pool usage (e.g. splashing) and environmental conditions (e.g. wind). The good news is that it doesn't really matter what the aeration rate is, you can still justifiably tell people that if they operate at lower pH then they will have more of a problem than if they operate at higher pH. Now it is certainly possible that they have such a low outgas rate already that the pH change won't show up visibly, but we know that if they go low enough then the outgassing will certainly occur -- otherwise, Ben's method to drop alkalinty wouldn't work reliably.

Hard to argue, especially since I am obviously waaay out of my knowledge base, but it seems to me that you are forgetting what effect swimmers might have on this closed system. Especially when you consider the contaminants they bring in which will in turn cause the chlorine to began to react. I also believe that debris (pollen, leaves dust) will also play a role.
There is no question that the external environmental effects will change the system and therefore the results. However, I believe it is better to understand the baseline "closed" system model as a starting point and then you can adjust that model, even qualitatively, to account for the factors that you mention. If this is either too hard or varies too much, then you can just throw up your hands on some issues, but I believe it's still worth trying to look at the pool and understand it as much as possible first and then only give up on those items that are too hard to figure out. I am also spoiled in my own pool situation because I have an electric (so it's easy to use and therefore covered most of the time) opaque (so UV doesn't get in) pool cover (that does not let air circulate underneath it) so my pool is much closer to being a closed system than most.

However, as far as the chlorine reacting with contaminants, be it ammonia or organics, it turns out that so long as you get to breakpoint with the ammonia and you oxidize the organics (i.e. you get to CC=0), then the chemistry that is involved turns out to have identical acidity as the breakdown of chlorine from sunlight and the breakdown of chlorine via temperature. Because all of these processes have an identical acidity effect, it doesn't really matter which one of them occurs or in what combination. If the chlorine all gets used up and you stay at CC=0, then the acidity of the process is predictable so the net effect with bleach is close to a net zero change in pH. Interestingly, a salt pool could start to see a chlorine outgas effect, especially at very low CYA or with no CYA, and this effect is very basic (i.e. causes a large increase in pH) and this effect would also be made more rapid by aeration and somewhat increased by lower pH, but mostly increased through very low to zero CYA and higher chlorine (FC) and salt (TDS). This is theory at this point as I have not heard of this effect in real pools yet (but then I have not heard of a salt pool with no CYA in it).

Now, of course, the junk that gets put into the pool may have a direct effect on the pH due to the pH of the junk that is put in and that is pretty much a total unknown. I believe that Evan (waterbear) mentioned on one thread about acid rain having an effect. Diligent users could actually make measurements of their rain water and actually predict what the change in their pool pH would be with various amounts (inches) of rain. I don't expect anyone to do this, of course. I'm just saying that there are things about the chemistry that can be understood even without going into the details.

As for the heater temperature, the difference in temperature that is relevant is the difference between the incoming pool water temperature of 82ºF and the outgoing temperature of 95ºF+ that you measured. The outside temperature of 74ºF is not relevent since the saturation index you would use would be based on pool temperature, not outside temperature. Anyway, you are finding a larger increase than is found in my pool, but I could only measure at the point of jets in my pool and there may be some (though I don't think that much) heat loss from the heater to my pool. I think the temperature difference is just a function of heater output and GPM and I probably have an overdesigned system with too high a GPM (though I have a solar system so maybe this is "reserve" power for when the solar panels are used -- I should probably have a 2-speed pump, but that's a whole other discussion).

Richard