About grounding the water of the aquarium. I think that it might be a good idea. But for safety you could use a resistor of about 1M ohm between the water and the ground. Use a large (long) resistor or use two resistors of 1M in series. The will avoid a static charge to build up.
Earthing the aquarium water has always been an interesting topic for me because on the one hand one might think it's better for the fish if any inducted
electricity is dissipated but on the other hand, it is used to "cover up" a more serious problem where there is an actual electrical fault leaking current into the watter - made even worse by the fact that there is no RCD or it has failed altogether.
Before doing this, it's probably best to figure out why you have stray currents in your setup. To do this, use a multimeter with it set to display VAC and then earth one lead and dip the other in the water. Chances are you will see some voltage there and in reality, it's more than likely that the equipment such your pumps are causing a bit of voltage due to inductance. This is nothing to be concerned about. However, you must do a second test with your multimeter. This time set it to measure current (Amperes) and then put one lead to earth and the other to water (make sure you change the leads on the meter if needed to measure A). At this point, if you see *ANY
* current flowing, you have a dangerous situation where there is actual current flowing from your tank to the earth. You need to then find the faulty piece of equipment by unplugging things until you see no more flow. Earthing in this situation is NOT recommended and you are only covering up a serious problem.