I think we need to take another look at what is actually happening and at least clear a couple of things up. He goes from watering once a week to twice a day - I've had plants in 20 oz cups for 2 months without watering twice a day or even once a day. How often are you watering/feeding them? that is the question at hand.
Edit - Yep, now that I go back and look, it definitely looks like its just too much water. also, why the water treatment, do you have hard water there? Do you have an ec/tds meter you could check your tap water with, or google the water report from the local supplier and see how much of what is in there, maybe you don't need to use it. I mean, how hard is it to let a bathtub of water sit for 24 hours? I got an 18 gal rubbermaid tub and hooked up a fishtank air supply and stone to bubble, I just keep fresh water in and don't water for 24 hours after filling, pretty easy rules to live by. Oh, and every week I'll add 1.25ml of 35%h2o2 per gallon to help preserve "freshness", lol!