you can mix salt and just throw a fish in
- thats the beauty of no rock and sand. Just want to make sure the water is not stagnant and has sufficient oxygen.
You will have no BIO filtration which is the biggest issue. so nothing will convert the ammonia to nitrates, etc. etc.
I would recommend this - (hopefully some seasoned reefers will have some input as well)
get a QT tank - standard 20 gallon
get a HOB filter - AC50 or AC70 works great and have enough flow that you dont need a power head
heater
air stone
do a water change in your main system. Take ten gallons of that dirty water plus ten gallons of fresh and use that to fill your QT tank.
the aquaclear filter inserts are pretty cheap so you can either just buy a pack of their pads and carbon and bio media or wing it yourself with some filter floss and a bag of carbon or chemi pure elite. If you choose to use the bio media that comes with the filter - just keep it in your sump when you arent running the QT then transfer it into the filter when you want to run a QT. That way you will have some bio filtration. Granted it wont be a lot but if you only keep a fish or two in there at a time it should suffice.
water changes will be very important. Atleast once a week (25%). siphon all the organics out of the bottom of the tank and replace teh filter floss in the filter. Dont change the other media.
