To answer your original question, I do not think that adding vinegar to your kalkwasser is decreasing the pH significantly. If my calculations are even ballpark correct, you aren't doing much to limit the pH increasing effects of kalkwasser dosing by adding vinegar. Rather, you're just jacking up the amount of CaOH you can dose in a given volume of water. So to answer your question earlier of whether 2 tsp of CaOH per gallon raises tank pH more than 3 tsp CaOH + 45 mL vinegar per gallon, your 3 tsp CaOH + vinegar probably raises tank pH more. The tradeoff is that when using vinegar, you can add more CaOH per gallon dosed. So per gallon, you raise your tank pH more with vinegar + extra CaOH, but per CaCO3 equivalent, you raise your pH less with vinegar + extra CaOH. The difference probably isn't that big though.
If you can, I would choose to increase your controlled dose of kalkwasser + vinegar. Here's my reasoning:
1) Unless you use a peristaltic pump for your ATO, dosing kalkwasser can seriously decrease the working life of a pump. This happened to my a couple years ago when I was dosing kalkwasser via ATO through a diaphragm pump. It failed after a couple months.
2) Dosing via ATO also limits how much evaporation you can counteract and prevents you from having consistent control over how much kalkwasser you're dosing. If it is a particularly dry and hot day, your tank might evaporate a lot more than normal. Your ATO would try to compensate, but if you're limiting your pH to some value (as you should), then your ATO would be forced to turn off prematurely and you wouldn't be able to keep up with evaporation. Additionally, while your evaporation rate is high, you'll be dosing much more kalk than while your evaporation rate is low. I don't think it is a good idea to let the amount of kalk you dose change that much based upon a parameter you can't control very well (evaporation).
Of course there is a practical limit to how much kalkwasser you can dose. It is limited by your evaporation rate and the rate at which CO2 can be sucked into your tank to lower the high pH generated by kalkwasser additions. If you really want to stick to dosing only kalkwasser for calcium and alkalinity additions, you can use some tricks to add more kalkwasser:
1) If the evaporation rate is limiting your kalkwasser additions, maximize evaporation rates by leaving as much water surface area uncovered as possible and running fans over the water. This will increase your water usage and electricity costs of course (due to adding more kalkwasser as extra top off and heating the water more to counteract evaporative cooling).
2) If high tank pH is limiting your kalkwasser additions, increase the uncovered water surface area of your system and add air pumps to increase the amount of CO2 your tank can capture. You can also try dripping your kalkwasser directly into your skimmer because all those bubbles contain CO2 from the air and that will help to lower your pH more quickly. However, if you have a recirculating skimmer, adding kalkwasser to it directly may also decrease the working life of your recirculating pump. If high pH is still limiting your kalkwasser additions, you can add a CO2 dosing system that will pump compressed CO2 directly into your skimmer or a CO2 reactor when the tank pH gets too high. This will lower your pH very effectively and should remove high tank pH as a limiting factor in kalkwasser dosing.
The thing is, if you're willing to go to all the trouble I just mentioned, you might as well start dosing 2 part or set up a calcium reactor. It really won't be more work to run a calcium reactor than it would to add a CO2 dosing system and dose extra kalkwasser. I think it would be easier to dose 2 part in addition to your kalkwasser. Sorry for the gigantic post, but that's my 2 cents.
