The tank is 55 gallons, was used as a fish tank for 5 years+ and has been sitting empty in my basement storage room for 4+years and I recently noticed that it is extremely dirty.
What is and what isn't safe to use when cleaning this tank in preparation for putting a Ball Python in it? It looks like mostly dust in it, but also some builtup that looks like dried salt, but it was used as a freshwater tank so not sure what it is.