What I would do is get a 15 gallon container and figure out the 10 gallon mark (empty one gallon jugs work for this). This way you have room for splash. if you used a a fish tank it will be filled to the brim and there would be spillage. Just my thoughts. I paid $5 for an 18 gallon tub (Wally World). I used it to clean my dead rock, but you would mix up 10 gallon or salt in it.