I have a couple of suggestions that I learned from shooting with my nikon 105 macro underwater in a housing. I have had the lens for years and was never happy with the results until i started paying attention to the aperture/depth of field settings, the focus mode (manual vs auto) and the lighting. If I want sharp images with maximum depth of field I set the aperture to as big (number) of an f stop as possible. I think your lens will shoot at f32. Of course this will probably not allow enough light in to the sensor to properly expose the subject. While I am shooting underwater, I have two 160 watt second strobes pointing directly at the subject on full ttl and that provides plenty of light and stops the subject if the subject is moving. In your display tank, if you have led lights that are not at 100% try increasing to 100% white for your shoot. If you try a strobe, you most likely will get light bounce back off the glass unless you have off camera strobe(s). The focus control is a bit harder underwater, but I would put your camera on a tripod and never hand hold. I think I see a bit of motion blur in some of your images of coral. Since the coral isn't moving, it is the camera/lens that is moving. A tripod will fix that problem. One last item, I looked up a tamron 90 macro. The lens i looked at had a minimum focus distance of 11.3 inches. Is it possible that you are getting too close to some of your subjects? I hope this helps some.
