The second sentence is trickier to interpret. Does it mean "An empty dive tank is allowed [in your checked baggage] with a USD150 USD200 fee each way"?Or does it mean "An empty dive tank is allowed [when checked as a separate item] with a USD150 USD200 fee each way"? Or does it not matter? I don't think it matters which way it's interpreted if the first sentence is interpreted as I did. If the first sentence is interpreted as prohibiting dive tanks in checked bags, then that means Delta wants to charge you a fee for empty tanks regardless of what bag the tank may or may not be packed in.
also, what is the charge...is it USD150 each way or USD200 each way?