in my limited experiance with volitans they seem to be rather stationary hunters, so i think you will probably be ok with this tank as far as dimensions and water volume go. but keep in mind that 'recommened' tank sizes for fish is assuming you have a standard rectangular aquarium. some fish require significant tank length for swimming, such as a sohol for example. so if it is 'recommended' that the sohol be in a 200 gallon aquarium, you still wouldn't want to put such a fish in a very tall but not so long aquarium.