See the tank won't be held up by 4-6 joist, but parrellel with 2 of them. Thats my problem. If the joists were running the other way on the house i would have no concern, but i have never seen someone run a tank or confirm it will be ok for 100-120gal tank. Otherwise Like i said i will just re-design a 60gal and work with that since i know people are running 55gals without any issues.
Here are some pictures of what i am dealing with.
i want the tank placed where the black couch is
my "joists" which are about 2 feet apart
Another idea of what the joist looks like
