The answer to the question on Bacteria is no, they do not survive being dried out. If the tank still has water in it, I would think twice about using it if you are changing over to sw.
If the tank was only recently a fw tank cleaning should be no problem. Get a friend and take it outside and hose it down and scrub out any accumulated dirt. Rinse it thoroughly. Do not use soap or chemicals.
Go to the grocery store and buy a product by Lysol called "food surface sanitizer". This stuff is a quat sanitizer like the sanitizers they use in hospitals and professional kitchens. Saltwater guys seem to be really fussy about bacteria
and I have to admit this is a prudent step. Spray the inside of the tank and let it air dry.
Then you are going to fill, adjust your water for sw or fw and do a fishless cycle.
Regards,
Jay
