I have had 4 (2 black neon and 2 black widows) fish die in the last 2 days and there are afew fish (more black widows a blue ram, Kuhli loach and more) looking very unhappy. i do water changes and test the water offen. just done a water change and tests but it seems to be fine but its not looking good at this stage, any ideas on what could be happing? or what i could do? all swimming very slow and i can pretty much pick them up if i wanted to