You need to be very very careful. You say you have a cichlid in your 10g whilst your 75g gets up to speed with the nitrogen cycle. You are slowly taking established media from your 10g to put in your 75g to give it a kickstart. If you're not careful your 10g could crash terribly putting your cichlid at risk. And in any case adding established media to a tank without fish, ie, a food source for your BB, is pointless anyway.
As already mentioned, it would have been wiser to move everything over to your 75g at once. Your BB in your 10g is already up to speed with the bio load your cichlid is creating so you should be ok, just don't be tempted to add anymore fish at this point.
When everything's transferred just keep tabs on your parameters then in your 75g. If you do experience any hiccup in parameters, and you are concerned for your fish, the simple way to eliminate the problem is to change out a % of water for fresh. Be sure to use your water conditioner.
Your 75g should settle down pretty quick.