Marine To Tropical Tank

@Stanster I have just done the same thing. I didnt do much othrr then a good cleaning with  akirchen scrubberto remove the crusty muck and salt deposits. I reused some of the substrate as a deep sand Nitrate filter and just gave it a dood wash The tank was scratched and also had a cloudy appearance in places so I tried to polish them ost but its a long job and not completely successful so have a good look before starting