Hey Lorne. I agree, 75 Gallons is too small for the lifetime of the loaches. But theoretically speaking 38 loaches in a 212 G tank have 5.6 G per loach space where 6 loaches in a 75 gallon will have double that at 12.5G each, if stocking levels are considered. Some of them can get to 16 inches in captivity but the average size in the wild is 8 inches from what I've read.