I have to move a holding female to a fry tank I'm going to buy. I currently have a 55 gal with two cascade 1000's. The 55 has a big bio load I'm guessing as it's stocked with 20 or so fish. In those cascade's I have two bags of bio rings in each, and one coarse sponge filter in each. Let's say I get a 20 gallon or so, how much media should I put in the new tank without hurting the old tank?