Also, don't forget the general rules for aquarium photography.
1) Make sure the aquarium glass is very, very clean.
2) Turn off all of your pumps, and allow everything to settle.
3) Turn off any other lights in the room. Also close all blinds, or preferrably wait until nighttime if you have any daylight seeping in (and you probably will if there are any windows around).
4) Shoot perpendicular to the glass (i.e. not at an agle).
5) Shoot from a steady platform. Ideally, that's a tripod, but even with an iphone or ipad, you can use something like a stool or chair to steady your hands as you shoot.
I'm sure I'm missing a few, but you get the idea. This still won't get you breathtaking photos with an iphone, but you should be able to get acceptable results.