Water

Hello. What you are doing is fine. Plants love oxygen on their roots too. A air bubbler works great to add more oxygen. I use, I guess their called a bartenders mixer. It has an electric moter and a little propeller at the other end. It will whip oxygen into the water in a few minutes. If you leave the water for 24 hours the oxygen will be just about depleted. Oxygen also dissipates chlorine. So I make my mix then blast it with oxygen and it's good to use. Hope that helps. Chuck.

Depends how long. Few days fine. Few weeks you could get mould growth depending on what's in the feed and if light gets to it or not.

Hi there. I've always prepared the soup at night, to give early morning before work leaving just to measure PH cause it stabilizes overnight also water chlorine can evaporate more and they grow just fine. So from my experience, leaving overnight is OK, but over a day...not really sure!

I usually get mine ready 24 hrs before I use it. Let it sit so all the chlorine goes, I usually mix my nutes in about 3 hours before feeding and set ph. I am thinking of putting a spare air stone in the bucket to keep it oxygenated. But I have never had a problem without the air stone.