Hey, these are good debates and good to be technical in this hobby. I think on your calculation you are short an inch. Most all tank sizes are for the outside measurements the 135.4 is 47.25 x 23.62 x 20.5 (I just measured mine - outside measurements). The sump is calculated the same as a total out side volume and the number 135 includes the ATO of 5.5. Now it is just a model number and I consider and call it my 90 gallon tank. I think we all agree that what's inside will look good. Cheers.I don't believe that calculator takes into account the actual height of water. This other site comes to 86 Gal with length and depth minus 1 inch for glass and 0.5" for bottom glass panel and 1" water height from edge which is being generous.... And once again not counting
What's lost from the overflow.