You would need a 125g or 150g tank to start. That will last you 2-3 years, depending on gar species (I'm assuming Florida gar). Above that, for life, either a 220g or 265g, because they need a big footprint. 5x2x2 is good, 5x2.5x2 would be better, 5x3x2 is best (middle number meaning front to back depth).