Hi, My betta fish has been lying on the bottom of his tank breathing very heavily. He's also been hanging around at the surface of the tank breathing gasping for air. When he goes to the surface sometimes he'll swim along whilst gasping for air as well. I'm really worried about him. He's in at 20 litre (5 gallon) tank and the temp is 26 degrees celsius. The ammonia and nitrate are 0ppm. I put in a methylene blue bath for 30 mins but it doesn't seem to have helped. Any ideas?? A few weeks ago he had velvet which showed up 2 days after I got him, I used acriflavine and methylene blue to successfully treat that, and left the acriflavine in for 2-3 weeks to be sure the velvet was gone. He then started fin biting (I saw him do it once) so its not fit rot. Its growing back quite well but he does seem to still be biting at them a bit, although not as much as before. I just don't know what's wrong with him really and why he keeps getting sick, any advice would be great! Thanks!