I have decided to upgrade to a 25-gallon tank from my active 10-gallon. This new tank is actually an old tank that I haven't used in a couple of years. I have old gravel that I have cleaned and made sure was good. My problem is it is a different color than the gravel that is in my smaller tank that is active right now. Is it safe to transfer my fish into the new tank if the gravel is completely different or will it stun them?