the electric fish need very clear and clean water. the ions in the water also make a difference to how they can emit the electrical pulses. I think poor water conditions (eg. dirty particulate water) hampers their ability to feel their way around their environment. they also use these electrical impulses to find other similar fish, and distinguish between sexes.
It's almost like a SONAR (like in submarines); obstructions in the water bounce back the signal to the transmitter ( the electric organ in the fish). with these fish (like the elephant nose) - the electric organ is toward the back of the fish and the receiver is in the front, so if there are obstructions in the water; the signal doesnt make it to the receiver - and this leads to complete disorientation.
(Imagine walking around in a small space blindfolded and banging into the walls constantly).
secondly if the electrical conductivity in the water is bad then the fish cannot survive as it cant transmit the electricity in the first place. (remember pure water [deionsied] cannot conduct electricity at all).
I once did a science experiment with 12 elephant noses when i was 15 - put them in a tank with the right sort of water for them - hooked up the anode and cathode to a very sensitive speaker which beeped everytime the fish sent a signal. it sounded like morse code. also (though im sure this is not very scientific) i noticed differences in the speed and frequency of beeps in responses to food, other fish and obstacles.
I then proceeded to put the elephant noses in my tank once the experiment was done! lol