What tank to move to the next?

In my time I have dealt with koi carp, silver sharks, tropical tank with guppies and neons assemblies. Now I have a 54 liters tank with 4 fancy goldfish and I really want to go back to owning fish full time. I'm thinking of getting a huge aquarium for the room 5 feet ahead perhaps m 2 tank, but I'm not sure what set to go. And I have cold water tank and not sure whether to go for a tropical aquarium or an aquarium salt water. What is needed to care for a saltwater aquarium? and what equipment is different from tropical and cold water tanks?

aquariums salt are much more complicated to maintain, but if you have been freshwater fish keeping for a while, and you think you are ready, go for it! Make sure you team knows that salt water tanks are quite expensive, so plan to spend hundreds of dollars. Believe it or not, starting with a larger tank is much easier because there is more room for error in the tank. 55 gallons or more would be a good size to start.

Shark Aquarium & Feeding- Custom Saltwater Aquariums by Living Color