so im upgrading from plain black gravel to eco-complete in my 2.5 nano. i bought 6lbs off of a member here. i pushed a good amount of the original gravel to one side and removed maybe 1/3 of the total amount of gravel. then i dropped in a divider and put about 2" of eco in. im figuring i'll do it in 2 steps so it doesnt make such a HUGE bio impact. is this a good idea? how long should i let the bacteria establish in the eco before i remove the remaining black gravel?