What are the basic gadgets I would require to set a marine home aquarium.?

Go to the website "About.com". There you will find a complete checklist of all the items you will need for a marine aquarium. If you do not have a lot of experience testing water, I would start a freshwater tank and see if you can keep it healthy for a while. A saltwater tank is much harder to maintain and needs almost constant attention to water quality, not just salinity.

An old saying in the aquarium trade is freshwater is hard to start up properly but easy to maintain once the nitrogen cycle is complete and saltwater is easy to start up but hard to maintain due to the marine fish needing perfect water quality to stay alive.

To start a 55 gallon marine tank, which is the smallest a beginner should start with, it will cost you in the neighborhood of $500.00.

You definantly need the Hydrometer but also a thermometer and, well, a fishtank heater to regulate the tropical temperature. A saltwater tank filter that will NOT filter out the salt(that would be bad) Oh yeah you need Aquarium salt, as regular salt kills fish and doesn't disolve right, and you need Fish. Rocks and plants help, but make sure they are clean and can live in saltwater. HAVE FUN!!

other than some decent test kits and the hydrometer (or refractometer if you want the most accurate salinity reading) , most likely a good skimmer. If you run live rock you can skip mechanical filtration but sooner or later most everyone goes to a skimmer in just about every type marine tank.

hrdyo meter to measure saltiny which can kill your fish or make the water the way they like it.