Funny as I do no scheduled water changes on my 120 or 45 frag.I agree, I’m going to stop water changes totally and screw all the salt companies
20 months on the 120 and only 3 10 gallon WC's.. I am doing 1 10gal every 4 months now.
45 frag system has had no WC since startup 14 months ago. Its going on the same once every 4 months soon.
So thats all off topic.
I have been using ESV for 5 years now and am very happy with it.
I do not go through much since I do minimal WC.
What I like about it is I can mix it up and its ready to go in 15 minutes.
However I do need to lower alk from 9.5 to 7 so that takes some extra time.
I am planning a upgrade of 3x my 120 and may use IO regular. I used it for years and it worked fine. If I set up a auto WC system I will have no problem using IO.
Stabilty with whatever you use is more important than what salt you use.
Pick one and stay with it.