Beach sand and Malawai cichlids

I have what should be a quick question, and I hope somebody might have some experience with this.

I just bought a 55 gallon tank off of eBay. It had been used previously as a saltwater tank, but was cleaned and then used as a display tank. After the cleaning, they put in some fresh sand, but never did anything with it. It looks, as far as I can tell like regular (South Florida) beach sand.

(click thumbnail for larger pic)

My plan is to make this tank into a Malawai cichlid tank. I know that these cichlids like sand. My question is, is this sand safe to use, or should I just clean it out and buy fresh sand from my LFS. If the answer is "it depends", what do I need to do to test and find out?

...And in case anyone's curious, this is Caesar. He is going to be one of the residents once it's all set up.

He deserves so much more than the 15 gallon he's in now (which is a step up from the 10 gallon pond he was in originally).

(Crossposted to cichlidfishes, aquaria, and my own journal.)