The reason a larger tank works well for a qt or ht is due to ammonia build up. The smaller the tank, the faster nh3 builds to stressful levels. This leaves you with daily water changes and stressing the fish makes them more susceptible to secondary afflictions. Plus it's like leaving a large dog in a crate for weeks at a time, it stresses them out and is not conducive to making them healthier.I have been doing alot of research on quarantine tanks, since I was going to make the old 29g biocube one. Why 20g for the quarantine tank? I see tons of well renowned recommending 10g tanks at the beginning.