AquariumLover;1278913; said:ok. so i get what you are saying for the most part, but if transitioning the filter media does not permit, how long must i run both filters before i can take the 29 gal filter out?
Hard to say since the old filter will continue to possess the bulk of the beneficial bacteria colony as long as the bioload remains constant. If you're not in a rush then try a fishless cycle on the 75gal and seed the tank with some of the biomedia from the 29gal. (you could also try filling a bucket with 1gal of tank water, remove the 29gal's filter media <temporarily> and swish and squeeze the media until the water is soiled <so to speak> then pour that water into the 75gal (which should already be containing dechlorinated water with the new filter running)...then feed that tank ammonia and everything else entailed in a fishless cycle).
What type of filter is on the 29gal and what type is intended for the 75?