When you put chlorine in water it combines with compounds in there to form monochloramine, adding more chlorine forms dichloramine, then even more chlorine forms trichloramine. What makes your eyes sore in a swimming pool is lack of chlorine and this causes the chloramines to move back to monochloramine. This is used in the USA to sanitise drinking water and is a disinfectant like chlorine itself. Aeration removes the chlorine and converts all the chloramines to monochloramine. It is removed by adding chemicals, not by aeration. If it burns your eyes in a swimming pool it can't make your fish feel particularly obejoyfull.