The deepest water we found SALs in was about 5 ft. Granted, we really didn't look in deeper water since out seine poles were only 8ft (and, none of us wanted to actually get into the water).
SALs do fine in large deep tanks. My last large one (3ft+) swam laps in the 520 and had no problem getting to the surface to breath. Just ensure no tankmates harass it as the LF is heading for the surface and it should be fine.