I fill two gallons of water and add dechlorinator and let them sit for a few days to get to room temp. This is what I fill their tanks with when I do a water change.
I don't remove the fish when I do a partial change.
I use an inexensive turkey baster to suck debris out of the gravel and suck out about half the water once a week. I rarely scrub the tanks out completely because good bacteria grows under the gravel- it won't suck up when you clean the gravel.
I don't use any sort of aquarium salts or medications in my tanks except for the dechlorinator and some betafix for my boy with torn fins. I think all else is overmedicating the tanks.
For food they get dried krill which is messy, small pellets, and I have a little bowl that I am trying to grow a batch of brine shrimp in from a children's learning store. I also give them mosquito larva when I find them in our pond.