This is what I did when my 100 gal had a small leak . I lowered the water down as tank was leaking just down from top aways. I set up new tank added used media from my old filter to the new filter added some of the gravel from the old tank I put it in nylons because I wanted sand in the new tank. I swished some more old media around in the new tank, I let it run for 48 hrs. I cycle all my tanks this way now and have had no probs whatsoever. ps I moved 20 fish at once to new tank and did not lose any. Hope this helps
