Anyone seen this before?

[HayleYoyo]

I have a guppy with a weird 'sac' attached to him.

Anyone seen it before?

He's been hiding all day. When jI fed him I saw it

[Filet_O_Fish]

Does it look like it's coming from the anal cavity? Sometimes it can be constipation, which would also explain the lethargy. What food do you provide the fish and do you alternate between different types?

Let us know how it goes.

[HayleYoyo]

I had fed him some flake food. For the most part, I've been fasting them. Their tank had a crash, and I have been keeping the food to a minimum until I can get the ammonia down.

Whatever it was disappeared maybe an hour after I took the photo.

I think it's fin rot. I've been dozing prime to detoxify the nitrogen