Have had an empty fish salt water filled 32 gal. aquarium for 4 yrs. How can I remove the salinity . Tank is permanently installed in living room wall. Have drained tank and refilled several times. Still the salt accumulates are clings to outer walls of tank. How do I remove the salt? Want a fresh water tank.:confused:

The build up you are experiencing is more than likely dust and mineral/hard water build up caused by evaporation.

If you have the original coral, crushed coral, rocks, or sand, etc for a salt water set up, these substrates will harden
The water as well causing the same effect during evaporation.

Both instances look very similar to salt build up that saltwater aquariums get.

Remove everything out of the aquarium, wipe and rinse, then replace with freshwater décor.

If the majority of the tank is enclosed, dust mixed with evaporating water will build up as well.
Wiping the tank and surrounding areas with a damp cloth often might be the only way to rid the problem.

Good luck.