Nice pics! I love the 1st one, looks like he is dancing haha.
I am curious about the ISO 100, if I use ISO 100 with my camera I need to slow the shutter speed way down and the pic comes out super blurry.
My shutter speed was at 1/80 lucky for me the fish held still long enough to get a crisp shot.
I also think the difference in the lenses comes into play here I used a 50mm prime lens while you used the kit lens, my lens has a larger aperture at an F stop of 1.8 versus the kit lens at 5.4 I believe that allowed me to use an ISO of 100. If you had more light you should be able to get a crisper shot with that high of an F-stop. Then again I could be totally off base I'm still very new to this so hopefully someone will correct me if I'm too far off.
The only light in the room was coming from the tank the room lights were off. I have 16 3w Led's lighting the tank so there was plenty of light.
I'm barely even an amateur with the camera I'm still learning about the settings I just tried small adjustments until the pics started to look better and then adjusted some more, must have taken well over 50 shots just to get those 3. I got so so at taking portraits of the kids but this tank photography is much more challenging so many reflections from the tank and subject matter that refuses to cooperate.