When seeding a tank, how long must you leave the old filter media in the new tank's filter?

Question

I have a 20 gal mature tank and set up a new 55 gallon this past weekend. My 20 gal has a small 5-10 gal aqua tech filter and a penguin 125. I took half the gravel from the 20 gal and placed it in the new tank and carbon cartridge from the aqua tech filter, i placed into the new filter for the new tank. The new one is acrylic and has no room for me to add the small filter directly to the tank. Now I have new fish in the 20 gallon and am wondering how long should I wait to put the carbon cartridge back into the proper filter on my established tank. Oh and the 55 gallon has 6 zebra danios and 9 cory cats in it, so there is an ammonia source. In my 20 gal the new fish started scratching for a day so I added meds. and treated for 3 days, during this time I had the carbon cartridge from the penguin in the new tanks filter also. I have since put it back in the 20 gallon.

Answer 1

I would leave the old filter for several days and then put in a new cartridge in your new filter. After that squeeze out the old cartridge into the filter, but behind the new filter cartidge so that some bacteria will be trapped in the new filter.

MM