Jose are you using the gutter and eggcrate setup for these shots? You're using 2 speedlites as well right? I'm trying to see if I can bite your style Hope you don't mind.
I love the exposure in your shots man. Nicely done. Now dont' hold back and teach me.
Ha thanks Nick! For this series all I did was set my speedlight up on my LED fixture pointing into the water, so about 15-18" off the water's surface. I set the zoom on the flash head to its widest angle (10mm) and put the diffuser cap on it. Flash was set to 1/3 manual power, triggered by my camera's built-in flash using the Commander mode.
Since I used only 1 speedlight and it was fairly high off the tank, I had to compensate with the settings. These were at f/8, 1/80th, and ISO 500. For these shots I tried to capture more ambient light so you could see the background. When I want photo background pitch black, I'll stop the settings down to approx f/16, 1/200th, and ISO 200, or so. That gives me results like this where everything is black except what is lit by the flash:
Hope that helps! This was just a quick shoot while I went home for lunch