Procedure
Fill your tank with fresh water from the source of your oysters. Our oysters come right from the Delaware Bay, so it's easy to gather a couple of jugs of bay water at the same time. You can create salt water with sea salt tablets. The salinity should be the same as that of the water that the oysters come from. 15 Parts seems to be standard, but you can check with your local pet supplier.
Allow the water to adjust to the tank. Oysters do better in warmer water. I usually allow it to sit an hour or so. Also, if you are going to use a water wall or similar device, the instructions often ask for them to be in the water for an hour before turning on the air pump.
The oysters will filter the tank on their own (remember: each oyster can filter up to 50 gallons a day!). However, oxygen needs to be added to the water or the oysters will die. I use a small air pump that plugs into the wall. The air hose is connected to the pump and then to the mist wall we have for our tank.
Once everything is hooked up and the water has adjusted to the tank, I place two oysters into the tank and turn on the air. Do not clean the oysters. The natural material on their shells will add to the environment. There will be algae and perhaps some parasites on the shells. This is good! If you have an aquarium light, use it for 8-12 hours a day. This will help the algae grow. If the algae sticks to the sides, you can scrape it off, but leave it in the tank.
If all is well with your tank, the oysters will filter the water. What was once brackish water will soon be clean. You will notice the oysters will open slightly. This is how they take in their nutrients. A gentle tap on the side of the aquarium will result with the oyster quickly shutting its valves. If the shells open widely, the oyster has died.