Converting saltwater to freshwater

[threephase37]

I bought a used running 47g show tank to get my feet wet on, come to find out it was in horrible shape. I tried to get the water back into check but the fact is I just didn't have the right equipment or cashflow to do so right now. It kills me cause after reading and learning the basics on here I got hooked on salt and I really want to get a 125g reef up and running over time, but cashflow prevents this at this time.
So, is it possable to take the 47g tank and substrate and convert it to a freshwater tank? What would I clean the substrate with to get the salt out of it? Freshwater is so much cheaper and I have to have something going for now.
Thanks for all the info and help you guys have gave me over time, I learned alot about equipment, levels, and basic keeping.

[Avi]

I don't think you should use the substrate from a saltwater tank in a freshwater aquarium. It's buffering tendency wouldn't be appropriate for most freshwater tropical fish. It's possible that you could use it after flushing it with a garden hose for a long time to clean it if you're only going to use it for African Cichlids, but I've never kept those and be sure that someone that has says that a marine substrate is even appropriate for them.

[Mithrax81]

The substrate would only be appropriate for African Cichlids. If you look into Tanganyikan cichlids in particular, they would be pretty cool for a tank that size IMO. Also, you wouldn't need to get 100% of the salt out ( a good rinse will do) since lake Tanganyika is slightly salty anyways.

I converted my first reef tank to a Tanganyikan tank for my parents when I left home for college years ago and it worked great.