Fear of falling through floor! Real or Not?

[Chin_Lee]

Before providing any advice, I will need more information such as:
1) age of the house,
2) spacing between floor joists (typically 12-16 inches)
3) width of floor joists (6/8/10/12 inches?)
4) placement of tank in relation to the floor joists (perpendicular or parallel)

If it helps any, my glass tank is a 160 gallon with approx 200lbs of live rock. Additional total weight should be around 1800-2000 lbs. My tank is placed in parallel with the joist (not the best) and the joist span between the two supporting walls is only about 12 feet. So it sits on three joists that are 12 inch wide and spaced 12 inches apart and at least one of them is a doubled joist. No problems so far.
To add to my assurance, I have had approximately 30-40 adults (additional minimum of 3000-4000 lbs) in the room around the tank for an entire afternoon and nothing happened.