Hi, I found a used tank I was looking to upgrade but was previously used as a reef tank. It has two overflows and am wondering what precautions I need to take to convert this tank from SW to FW. Is there any specific cleaning agents I should use to make sure the tank is as clean and uncontaminated as possible? Is residue left over from a saltwater reef tank dangerous to freshwater fish (aro, PB, CL) thanks.