I did for my 10g tank a while back. I figured the costs of bulbs, additives, salt, power, water, food...everything. That 10g tank, alone, averaged $20 per month. I decided I didn't want to know what the 40g would cost. Now I'm up to an 8g, 10g, 55g, and 150g. If I totalled it up, I probably wouldn't have tanks anymore...either that...or a spouse!