Hi guys, new on here and relatively new to fish keeping. Have quite a small tropical tank, 5 tetras, male fighter, couple of loaches, and I did have 5 swordtails, all fish have been fine apart from swordtails which have one by one died off. Have two left this morning has just died and now that is showing to same signs of distress. Top fin down flat on its back, loss of colour, bombing the gravel. All other fish in tank fine including the other swordtail. Apologies for long rant, anyone could help I'd appreciate it. (Last water change 20% 3 days ago) thanks, dan