I know your upset and frustrated , the people here are trying to help you . That being said make a check list starting with all your parameters and if their in check look at the possibility that there may be stray voltage. Next check for the quality of the water coming from the tap into your RO system . Check for heavy clorimines . Icp test can be helpful . If so add clorimine filters inline with your RO after the sediment filter . You mentioned possible rust which can be a issue , check all metals in contact with your tank including and especially magnets . All it takes is one drop on the floor and the plastic gets a unseen hairline crack that allows the magnet to rust . Are you running a UV light ??? Wouldn’t hurt if it’s something in the water column disease / parasitic wise ? . Being a small tank is your water that your changing the same temp ?? Could it be shocking the tank ? If your keeping your parameters stable and run down the list your bound to find the problem . Also as far as the clicking , my snails do that often not sure if you have them but that could be a source for the clicking as they go up near the surface . Hope this helps but I would step back make a check list after reading the post written here as suggestions . It is a great hobby until something goes wrong . There is still a lot not known about recreating the ocean in a small see thru box but on the other hand this hobby has come a long way in the last 15 years compared to when I started . Good luck !!!