Thank you guys !!
Let's see if I can make myself understood !!!
This system is characteristic declines and rising in the corners of the aquarium.
The illustration shown in post Bent, shows four boxes on the glass bottom, but that's not the only way to be done ... in the case of my tank I had the impossibility of 4 boxes, then did an internal channel joining the 3 falls in one box ...... with that the aquarium was with two boxes, one for the ascent and another for the return of water.
*
Normally do this kind of aquarium with glasses a little thicker than normal because it is a rimless aquarium and a few holes in the bottom glass ...
We never had cracking problems doing that way.
The aquarium rack openings are made to position the boxes.
Sorry guys, not properly speak English, and often use the Google translator.
Thank you for joining the topic !!
Hugs !!