Very nice tank.
Try shooting in Raw then play with reducing exposure and brightness. You can also underexpose and then increase esposure as it's always better to correct a darker image than an overexposed one as when you clipp the highlights data is lost. Still it's not really too much overexposed so I think if you cut down just a bit on your exposure and then play in PP you might save it.
you can also try the shadow Highlight tool in PS on a less over exposed JPEG.
What lighting do you have on that tank and why is the Lt side much more overexposed than the Rt? I f you have a MH or an intense bulb there maybe putting a filter in front of it while taking pictures could even things out, Still you'll have to find some filters and play with how many ones you want in front of it to have the correct attenuation.
Other things i Could try but not really sure if they'll help or not:
a Polarizer, or a graduated density filter. not the circular filters that snap on the lense but the square ones that go on a holder that you attach on your lens. Cookin makes some of those with their holders as well as rings to fit the holder on your lens thread. They are cheap and the advantage is that you can slide those up or down so that you have different densities till you have the correct gradual attenuation that deals with overexposed top witout making it too dark and also does not make the bottom too dark. They have many filters but I think your best bet would be either the gradual blue or Grey you might still have to try the soft and hard transition ones. these will not correct the image as you'll always have that overexposure under the birght light, however it'll minimize the amount of highlight clipping that is taking place and you'll have better chance to fixe that in PP.
In PP maybe creating a gradual mask on a layer above the first one then playing with the mask opacity till things look better.. Still your starting picture should be a bit less exposed than this.
