If you consider extra space for your tanks "wasting" it, you don't care for your fish like I care for mine. I am phasing out my fifteens in favor of twenties. You will have better luck with your fish in larger tanks too because, let's face it, it isn't luck. Try fewer, larger tanks and fewer kinds of fish of better quality with a better quality of life. I know that's easy to say and hard to do but 10's are awful small.