Oh, I guess I'll also throw in my setup. It's not done yet, but I'll try to remember to post a picture once it's all set up. I'll be using two dosing pumps. One will be dialed in to do 24/7 topping off of the tank as water evaporates out. The other will be used for a 24/7 drip into my kalk reactor, which then will dose kalk 24/7 into the sump. I know lots of people run their topoff systems through the kalk reactor, but I want to be 100% sure of the amount of kalk going into the tank. So, for me that involves two pumps. Not quite as "pretty" as a setup using a sensor to control topoff, but I hope that doing 24/7 drips will help to make the water parameters rock solid and give me the peace of mind knowing exactly what's going into the tank and how often.
Once again, I'll try to post a picture when it's set up. I've got all the pumps and supplies in my basement, I just need to find the couple hours to set everything up and make sure it's running properly.
-Joe