My sanchezi rarely uses all of his 100gallon tank, mostly just stays on one side hanging out behind a log. He comes out to harass me if he sees me sitting or walking by, he always wants to be fed even after he just got fed. I feed him shrimp, mahi mahi and he literally comes up to the surface and waits for me to drop in the pieces and snatches them as soon as they hit the water. Every once in a while he will patrol the whole length of the tank usually at dawn or dusk before the tank lights come on when theres a bit of natural light. Other then that he rarely uses the full length, I think a 75g would be fine for him even at his current size I think hes right about 8" and 16 years old. He was very active at the 3" size swimming the full length of the front glass but tends to just chill the bigger he got. Even a 55g would be fine for a sanchezi until they get up to the 7"+ range then I could see them needing a wider tank not necessarily longer. Just my opinion.