You use hot water to fill? The problem is that the hot water tank frequently had harder water/mineral buildup compared to the cold water line. May not be an issue, but I don't fill with hot water at all.
Btw, it's not residue in the softener tank, it's how it works. There is an ion exchange, leaving sodium (not "salt") in the water as it removes the hard water minerals.
You use no hot water at all filling your tank? The cold water coming into my house is 46 degrees right now. There is no way you could fill a tank and not shock the hell out of the fish with that. You have to use some hot water to atleast get it to a suitable temperature to re-fill a tank.
And as I stated I was told it was sodium something that was left behind. And I guess this "sodium something" is what is bad for plants. However I cant seem to find a straight answer on this. There are those that have a setup like mine and use straight tap water. And there are those that hav e asetup like mine and use an RO/DI unit. So which way do you go?