Figure 8 Pufferfish

[nathcroft]

hi all,i'm new to this site and have been keeping freshwater tropical community tanks for nearly ten yrs now.i purchased a pair of figure 8 pufferfish about a year ago and apart from them being a bit nippy and domineering to start with and having a few deaths which i attributed to the puffers(i was not given the correct information from where i purchased them as to how to keep and feed them)this i eventually found out from researching about them.in the last 2 weeks one seems to have developed a problem,it seems very bloated i am wondering if the fish is constipated or has possibly got dropsy(but the scales look fine rather than protruding out)in itself it seems ok ,i have cut feeding down completely since yesterday as it won't harm the fish to have a period to go without,and this morning i noticed it's right eye has a white spot on it that looks similar to a cataract.now i'm worried the other strange thing i noticed was it was swimming up and down the tank in a near vertical line getting to the top and then going to the bottom this has been more repetitive today!my water values for ph =7 am=0 no2=0 and no3=0 and these have remained constant since i have had the tank which is 65 litres and there is plenty of real plant and an internal filter and heater and plenty of line of sight breaks and hidey holes so they can all get out of the way if they wish and have all lived in relative harmony.i feed flake,frozen bloodworms,frozen mussels and cat fish pellets for the bottom feeders.no new fish have been introduced into the tank for at least 6 months so i don't believe it's something thats been introduced into the tank.please help i'm at my wits end and desperate need of advice