I had a 20 gallon and a 45 hex for a few years a long time ago. The 20 ended up being a self sustaining eco system until a cat broke the mercury thermometer. The 45 died in a transfer when the bottom broke. I've had a 120 for 10 years, but it was always a hot mess. I finally broke it down 6 months ago and was done, until a 2 Inch clown was discovered in my overflow. I moved it and 2 retrieved fish from my lfs to my 30 sump and the sump became my test to staying in the hobby. For the 4th month, everything is perfect except the phosphates. My tank currently holds 2 perculas, 1 false lemon peel angel, 2 skunk cleaners, 6 zebra snails, a pistol shrimp and aurora goby, 6 blue leg hermits, green bubble tip, and a short spine urchin. I've got a plan to get a much larger tank running in September.