I am thinking about removing the substrste in my 75g tank and replacing it with sand or some fine gravel so that I can add some loaches. My question is if I replace the substrate will I need to cycle the tank all over again? I was thinking about leaving an inch of the gravel to seed the new tank. Does any one know how deep dojo loaches burrow? I don't want to cap the gravel just to have the loaches mix the two substrates together. The tank has been up and running for almost a year.