Hey there and welcome to aquarium advice! I understand you, and i think most aquarists do too! Its the tank syndrome, you buy one aquarium and can never get enough so you need another one. Its quite fulfilling though! I started with a 2 gallon(with goldfish, oh me!) And now i have a 125. I used to own a 220 which i should get back shortly. I do not own any smaller tanks than 55 though because im not a smaller fish type guy
anyways good luck!
55 Gallon- Empty
125 Gallon- CKF and Tiger Oscar
220 Gallon- To come...