The easiest way to keep a quar or med tank ready is actually empty. Run an additional small filter on your main tank, or have some extra media in your main filter that will fit in the smaller filter for the smaller tank. When you have new purchases, or an ill fish, fill the quar tank, many use half tank water from the main tank & half tap water. Add the heater, make sure the smaller tank water is the proper temperature, add the fish & set up the filter. Some water movement is needed, convection works vertically, tanks are usually more horizontally oriented.
When you are done with the smaller tank, add the healed or new fish back to the intended tank, and take down the smaller tank. In the event of a sick fish that doesn't survive it's advisable to throw out the filter media & clean the tank, along with any other items that were in contact with the water such as the filter case or heater, with a solution of 1 part bleach to 20 parts water.
As far as light, room light is fine, dimmer light actually makes fish feel more comfortable when stressed. as when in new surroundings. Depending on the fish, a few caves or plants may make them feel more secure. Bare bottom tanks work better as they are easier to keep clean.
I quar new fish from 2 to 4 weeks. If the water in the quar tank is basically the same as water in the tank you plan on keeping them in long term, a little netting causes less stress than would be found in the wild. I move fish from tank to tank on a regular basis. They go in the same water thay came out of within seconds, and are soon fed the same food. This bothers them anywhere from not at all to being a little apprehensive of their new suroundings for a few hours.
Also; If it concerns the original post & helps the original poster, I don't see how it can hurt anything.
