I tried to cure the fish follow the instructions, but he died. [on_024] Fish's head was real red. I think it was blood inside. Thank you for every instructions.
Your tank may have a couple problems, so here is a few ideas to consider.
1) 28 -29 degrees is really warm. Try to put the tank in a cooler location. Tanks on the lower level is always cooler than on the top shelf. Warmer temperatures increases the growth rate for bacteria which can make the tank go bad quicker
2) It sounds like your tank isn't biologically balanced which can cause stress to the fish. Can you post a picture of your tank so I can see the design?? Adding live plants helps maintain water quality. Adding fish/shrimp that control Bio-film helps a lot too....such as Otocinclus, Panamanse and shrimps.
3) Giving the fish places to hide helps to reduce stress in the fish which helps them to maintain a good immune system. Adding plants and wood creates those hiding places. Also, make sure the sand/gravel you use is a rounded type. Angular/sharp substrate scratches the fish and promotes infections too.
I hope this helps. If someone could translate this into Thai it would be a appreciated by more people.