what kind of wood is it? i have mopani in my tank and i got it from another member on here who had it in his tank for almost year and now its been in my tank for almost a year and it still leaches tannins, when i first put it in my tank it would leach really badly and would turn my tank water a dark reddish color but its just tannins its nothing bad for the fish, and they actually like it because it helps to buffer the water to a lower pH. some people actually purposely add these tannins to their tank. but what are your water parameters (actual numbers) and how often do you water changes? it definitely sounds like some kind of infection or swim bladder problem if he isnt swimming properly, there is a difference between fish swimming and shaking and "dancing" when breeding, etc and then being sick and not being able to keep themselves level which it sounds like what is wrong with your con