Nice pics...as an amateur photographer(talking about myself here lol), let me make a couple of suggestions I am sure you already know.
When shooting with this macro lens, you should only do so in manual mode. You'll need to play with the Fstop , Iso, and whitebalance to get the right colors to show.
Yours pics look overexposed which is due to the aquarium lighting, so you need to reduce your shutter and maybe play with iso til you get a good pic. Make sure to use a tripod and remote.
I realize this is just the first attempts, but just trying to make the learning curve faster for you
I was in the same boat as you not long ago, heck I am still learning lol.
Of course you can process the pics after shooting as well, but its nice to find all the right settings before you need to process, to save you time. Work on the white balance, f-stop, and iso settings. Also, if you haven't already, get a nice circular polarizing lens.
Otherwise, lookin good