Sometimes it can be frustrating when fish die out of nowhere and die so fast even when doing the right thing. Recently I purchased 6 small Harlequin Rasboras and they all died within 3 hours. It is a very well filtered cycled 20 long and I do all appropriate water changes. I have a betta living in there and he has been in and doing well for 3 months! I tried other tetras/barbs in there and they all started dying so I had to save them by moving them to outside ponds! I think what might be killing them is an aquarium ornament I purchased from Walmart!!! I removed the ornament tonight and it has a strange rubber smell! It upsets me but what am I supposed to do? Stuff like this makes me want to quit but I have to keep my head up. Oh and the plants in my tank have been thriving despite all this he## I am going through, I pick up the dead fish bodies once they die.