I have had my betta for four months in a cycled 5 gallon filtered/heated tank with live plants. A month ago his dorsal fin began to shrivel and a black spot appeared in the middle (see pictures). I think it is fin rot, but all the sources I've seen on fin rot says it starts at the edges of the fins and not in the middle or near the base. It wasn't getting better with daily water changes. I have been dosing Paraguard for the last week, but it doesn't seem to be doing much. In the last two days my betta has stopped swimming and eating. He seems like he is in pain when he swims up to the surface for air. The black area is getting noticeably bigger with each passing day and has spread to the upper middle edge of his tail fin. I am worried my betta will die very soon. Any help at all in diagnosing this will help me decide what treatment I can pursue. Please help me!!!!