There are many ways to go about setting up a brackish water aquarium, all of them relatively easy.
Q. I would like to set up a brackish tank with puffers, scats and some sharks. What size tank do you recommend, and how should it be set up before adding the fish?
A. There are many ways to go about setting up a brackish water aquarium, all of them relatively easy. Choose an aquarium that is suitable for a marine environment. Any metal, such as in light fixtures and hoods, will corrode if allowed to come in contact with salt water. Brackish water fish also require more room than we generally provide for freshwater species.
The aquarium should be as large as you can afford and have space for. In fact, for all practical purposes, you can approach a brackish water tank as you would a marine tank, using equipment and accessories that would be suitable for a saltwater aquarium. Aquascaping the tank, however, is best accomplished by thinking of a freshwater aquarium with large cichlids. This means large rocks, treated driftwood and artificial plants.
Mixing water for a brackish tank is simple. Create a stock solution by using a good-quality synthetic saltwater mix and adding this water to freshwater at a 10 to 1 ratio. When adding to a tank with fish already in it, mix the water in another aquarium or container before adding to the tank. Because salt does not evaporate, use freshwater when adding replacement water for evaporation. For water changes, you can use your stock solution.
You should acquire as much reference material on the fish you plan to keep as you can find. For example, not all puffers are brackish water fish — some do not do well in saltwater. Scats and monos (Monodactylus) are excellent choices for this type of aquarium. I'm not sure what you mean by sharks. All of the species of sharks I know of that are small enough to fit in a home aquarium are strictly marine animals, and most of the fish in the hobby that are referred to as sharks (such as the redtail shark) are strictly freshwater species. Choose your fish carefully!