Thanks for the pointers, i used a macro ring flash and still figuring out how to reduce the brightness. The reflection is a bit of a problem with it, but also couldnt get as much detail without it. Any tips with a ring flash?
I used to use a macro ring back when I used a 35mm. Since switching to digital, I haven't experimented with it (that's what happens when you switch from Canon to Nikon and your equipment becomes useless, haha).
That being said...I haven't had the chance to play around with the white balance in combination with the ring flash. There's a chance that if you manually adjust your white balance settings, you may be able to get a bit more detail in the whites. BUT, I think the main issue that you're having is really just the direct flash combined with the fact that you are shooting a subject that's highly reflective.
The unfortunate disadvantage of the ring flash is that you usually lose the ability to control the intensity of the flash...I know this was the case with my canon...it basically shutoff the controls on the shoe mounted unit. So...you have a couple options.
1) Go back to the shoe mounted flash, ditching the ring flash. Angle the shoe mount upwards and bounce it off a reflective surface above the tank. White posterboard works fine for this...and if you don't have a volunteer to hold it for you, just rig it up some way. It can be awkward, but it works, and is cheaper than buying a fancy umbrella or light box.
Who want's to ditch a fancy ring flash though
2) Keep using the ring flash, but instead of mounting it on the lens, use a bracket and mount it above the camera, at about 45 degrees to the tank like I mentioned. If the cord is long enough...you basically already have a (wired) remote flash to put to use. I dunno if you're shooting with a tripod already...but if you happen to have a spare one, it's pretty easy to just hang it somewhere on the tripod and go to town. I've used a ziptie in the past and it's worked out great.
I have some 35mm prints that I shot like this at an aquarium in Spain...without a macro lens. I'll see if I can "take a picture of the picture" with any luck. If I can, I'll upload those and show you the results. Since you can't adjust the intensity from the shoe mount, all you have to do is play around with the distance and angle to compromise for that, and it makes a noticeable difference.
As I said though, impressive pics...you're making me want to get back into macro after shooting landscapes and portraits for the past several years. Once you get dialed in with the settings, macro can be a lot of fun.