Hey, we have 2 4 Year old goldfish (Moby & Clive) who are very healthy, sociable etc and have great appetites. Recently, (Moby especially) keeps taking mini 'fits'. He starts thrashing around the tank throwing his head from side to side banging into the side of the tank, gravel, stones etc - and more recently, he has started to flip out the water (we have a 180 litre tank) and manages to hit the top of the tank so hard, the lid lifts up a bit! He seems ok after the fit has passed but we are worried incase he does hurt himself, or manages to shatter the strip light in the tank as it is at the top of the tank. Can anyone advise if they have had this problem, and if there is a cure, or is it just natural? Thanks!