I have a bunch of this gravel left over from whem my 55 US Gallon aquarium was fresh water. I don't want to throw it out because it's good looking gravel, and I'll use it again if I ever set up another freshwater system. In the mean time, would it be good, bad, or neither to put it in my sump to let the water flow over and through it? Would it grow the needed biology to act as additional biological filtration, or just become poison?