I use plain tap, the softened water was an accident. It uses too much softener salt. That being said, I would not hesitate to use softened water for growing out fish if that was all that was available.
Not sure I follow the sodium build up thing. Do you mean in the fish or in the water?
I agree that using Bypass will resolve the issue, but yes repeated usage of bypass valve might damage it causing leak. I think I will take the extra effort by adding some regular water (aged and heated) from the garden hose unit. Since its first floor will be using a couple buckets and rest will be tap water(soft). Will occasionally add some minerals as well probably once a week! Thanks everyone.
For the tank on the second floor ? its possible, but maybe extra money hiring a plumber. I did decide to move the tanks from my office on the second floor (sucks!) but I guess giving the babies water they need is what I need to watch out. First floor I have access to cold water which I will be aging it and heating the water. So I guess its good !
I have a softener and occasionally i leave the bypass and fill a couple gallons of softened water to my tank and havent noticed any ill effects. The other thing you can use which i have read doesnt hurt the fish is switching from sodium chloride, the regular salt, to potassium chloride. Your fish and plants can use the extra potassium and depending on how hard your water is may or may not be super high.