it's not the water, or water conditions. i've had this problem in last house in glenfield now i'm in milford same thing. it only started 10 months ago, i've been keeping fish for around 5 years. also, my other fish are sweet, convict is super active and very colourful, jag is colouring up nicely, all other fish are acting normal. it's just that every now and then, one fish starts acting drunk and is dead within hours. sometimes the scales fall off them, sometimes nothing seems wrong with them. it's really quite frustrating.