Hi All I've just spent ages searching Google but to no avail.. I'm at a loss. I've lost a few fish very unexpectedly.. they've seemed absolutely fine, then the next time I see the tank they've gone.. I was convinced it was my tap water (I've had problems with it before) so last weekend did a full gravel replacement, kept half of the water back and refilled with half old half new. I've kept my eye on water parameters and no probs at all. Tank looks super healthy, fish great.. Got in from work and put tank lights on, all fine.. 1 hour later i've a dead dwarf rainbow that i've had for around 2 years. No sign of illness at all. All I can think it to be now is a parasite (unless it's just an unlucky coincidence). So I'm really worried about my discus.. my large male discus has translucent poo. No behavioural signs that anything is wrong but I'm really worried it's something internal that's killing the fish. I had camallanus worms in the tank around 8 months ago which I think came in with a couple of rams. I lost the rams but tank was treated twice over with meds to be safe. Since the worms I religiously check my fish every night for signs of them but haven't seen any sticking out of the fish. Does anyone have any ideas what it could be? I have no clue what else I can do. I have shrimp so can't treat the tank with a lot of meds unless I separate them. Any advice would be greatly appreciated.