Where is the best location for a circulation pump inside a reef tank?

usually the left and right corners are pretty good,

if it is a very small reef and you have a pump that can keep a slow moving current then you should put it on either the left or right side of the tank, towards the back of the tank, if you have high stacked live rock then put it high and if you have low rock put it low. Then put your return on the opposite side of the tank (unless you have a overflow than move the powerhead to the other side)

Now if you have a larger tank than a 40 long and up you should have at least 2 power heads and Kitty corner from each other with one placed a little lower then the other.

good luck =)

To get enough circulation in a reef tank, you'll probably have to have more than one powerhead or water return. I try to place mine so that there aren't any dead spots, but its a challenge. I have several returns from various equipment on the back of my tank, and I have two powerheads in the top,front corners pointing down and towards the rear of the tank. With the arrangement of live rock that I have, this seems to work decently well. However, there's no such thing as too much water movement until your corals are unhappy. Remember, the ocean has some serious circulation, and it would be tough to even get close to that.