How long can we keep 35 gallon of pre mixed nutes

Good question I thought about this too, for sure a air stone would be beneficial i would think so it doesnt get stagnant

Yes. I usely mix a concentrate which I add 1 cup to 5 gallons of water. I then mix 30 gallons in a main reservoir which feeds several different reservoirs.

To prevent precipitation, I've been told and observed keeping base, MagSulfate, and calcium Ammonia Nitrates separate is the way to go..usually see precipitation within base that contains all 3 and others, as a solution, within 3 days. Keep separate or in moving water to avoid.

I usually mix up a 200 litre drum of premixed nutrient solution to use during the week when topping up my systems.

Keep a bubbler in the bottom and light out and you are all set.

That is fine, just make sure to check water temp, always have an airstone going, and chemck the ppms. How long you can use the nutes depends on you ppms. If your ppms get out of adjustment as well as your ph, adjust accordingly. The plants will be feeding, so thus your ph and ppms will need adjustment.

Depends on the nutrients.