There is a couple of points I would like to add here. I worked at my local fish store for about 7 years through high school and college (which I still frequent and talk with customers I used to help) and dealing with a variety of situations I have some advice I'd like to offer to you.
1. Maintaining equipment- I know you have said it a bunch that you like your tech, which is great and can be super powerful but like anything else they are only as good as you program them to be (which requires a certain skill set). The tech is great but it never hurts to run a manual test to confirm your pumps/testers are performing how they should (I recently found out my reagent for my Hanna alkalinity tester was no good and it was measuring 1dkh high, which for a sps tank isn’t good).
2. With kalk you will find some people that swear by it and others that want nothing to do with it. Personally, I do not like using Kalk for a few reasons but mostly the fact that I live in PA and my evaporation varies depending on the season makes it really hard to maintain a constant dose level. So in the winter when the heat is running my ato will be running more, adding more freshwater (and in this case more Kalk, where my system might not need it causing a spike in CA & KH). Kalk is also hard on the pumps and requires more upkeep in clearing the lines and the storage containers (it does settle out so it needs to be mixed often to maintain the solution). Also for your setup, I'm not sure if I missed it or not but I didn't see any way for you to dose it. Most people have a top-off container where they mix the kalk into solution and an ato pumps it to the tank as part of the top-off procedure.
3. Unlimited RO water access for top-off
I have dealt with a few cases where people hook their tanks directly up to the RO system and a float switches fails & pumps endless amounts of freshwater into the tank and the floor, or a drain clogs and your return pump keeps pumping into the display drains the sump and the ro unit pushes water to the tank, again turning your tank into a freshwater tank. Lastly when a ro unit has sat idle for any amount of time before you begin using the water it is making you should purge the membrane (ex. run the water coming from the membrane into the drain for a minute or two). Doing this will also preserve your DI resin as it does not have to work as hard removing what settled in the membrane. A DI canister (attached to your ro unit) and an inline TDS meter is the next thing I would invest in which will cost you approximately $150. These are your first line of defense when it comes to battling nitrates and phosphates coming in from the tap water. Back to my point of unlimited access to water, I would consider a separate container (~20-30 gals) to store your freshwater that you can turn the ro on fill the container then turn the ro off. This separates your tank from a direct line to water but then you will need to purchase an ato. Maybe even look into mixing station, there are lots of threads on here of people sharing their setups and advice.
4. Each tank is different and responds differently to any changes you make. So keep this in mind what works for some may not work for your tank. You have to make adjustments based on what your tank is telling you visually (there are somethings that you can't test for) and from testing parameters. This is all part of the learning curve and the fun of the hobby.
Sorry for the dissertation but I hope this offers you some advice. Good luck with your build. Feel free to message me with any questions!
