My 3 Green Corys do something very strange and a Syno. Petricola I used to own would do this as well so I would imagine its not just a Cory Cat thing. Heres the deal. Every time I do a water change (30-40% 1x a week) they act like they are "dying". Swimming irraticaly (Like the dreaded death spin) or just laying on the bottom, often on there sides, fins clamped, sometimes pinning themselves behind a rock or the heater. It freaks me out as I worry im gonna lose them. However, shortly after they go back to their old selves acting like nothing ever happened. Is this a normal catfish thing? None of my other fish (Tetras, Angels etc.) seem to be bothered.