The 'german' method (although thats probably not what it's really called
) is just taking out the top third of the substrate and then mixing the remaining substrate in with new. So essentially what you're doing
. It's a good idea taking the bottom layers of substrate out, cleaning the base and then putting it back in. I hadn't thought of doing it that way, I may try it. I think I just feel better changing everything out since I do leave it for 3 months at a time and with the Fitch a big bag lasts a year so I don't really feel the need to be frugal with it. Since I sprinkle used but clean substrate over all the fresh stuff Spike doesn't seem too bothered. He is usually a bit cautious while he checks out the cage to make sure everything is where it's supposed to be and then it's back to business as usual
