This little fish is in a bad way, I think. Originally I thought it was a female about to lay eggs but 2 days later, this evening I could see she looked awful.
Haven't noticed any other problems with the other fish.
I was thinking internal parasites or backed up eggs. It's tummy looks 2x as big as it should be. sorry for the bad pic. I have never had experience for either problem.
Haven't noticed any stringy poop, or worms or dots on the fish. It is well colored though looks washed out in the pic due to lighting and the poor camera.
The water params
between 20 & 30 Nitrates