i want a really big and nice tank, i have worked with sharks and know how to take care of them, i worked in an aquarium for 2.5 years and i have been going back to the aquarium since wich was 3 years ago when i left so i have alot of experiance with the sharks and other fish.

so how big would the tank need to be for them all to be happy and grow to full size, i have heard that black tips live happily in 1500 gallon tanks which i dont know how big a 1500 gallon is or how much a gallon is to a litre, and also how big would a 5000 gallon tank be in feet or meters.

and how is it that people have such big tanks but they dont seem to take much maintinence, because you need a 1/3 water change every 2 weeks which if you have a 1500 gallon tank thats 500 gallons of what you need to take out every 2 weeks and put back in which could also kill the sharks from the fast temperature change if not done right, the salt also needs to be checked regually and the temperature needs to be check regulally, and what do they do if theres a black out or they want to go on holidays for a few weeks, so please answer as many questions as you can please, thankyou
by 2000 fish i mean small fish and thats probably an exajeration but still, and i asked what size tank not saying is this big enough