I'm not sure, but I think an anechoic chamber is a different, more deprived, experience. I've been in the one at NPS in Monterey, and it's a very strange experience. No echos, no external sounds, no vibrations, still body temp air, and no light. In a water tank, you still hear the water, feel the edges of the tank, feel the water move when you move your body, etc, right?