What’s wrong with this CPD?

[memorywrangler]

What’s wrong with this fish?

Looks like it does in the photo. Lethargic.

Chlorine -0
Ammonia -0
Nitrates 10ppm
Nitrites 0
76F

Tanks been up for a year with no recent changes or problems.  Tank mates are CPDs, 3 male guppies, and a pretty chill betta.

I had a bought of _something_ that was killing guppies about 14 months ago.  I tried probably 5 antibiotics, and nothing worked.  I’m not excited to start down that road again unless I have some decent idea of what it is.

Does anyone ever successfully treat a fish this sick?

[CJs Aquatics]

@Colu

[Colu]

Looks weak any rapid breathing listlessness flashing spitting food out loss of appetite it might be the way his body is bent it looks like it has a bit of a sunken belly correct me if am wrong on that @memorywrangler

[Guppysnail]

I have bred CPD for a few years. I often get new kids to keep genetics fresh. I have seen this in new kids and a few times in mine. 
Causes for my kids were bullying. Males were always the affected ones. I successfully separated and fed very well 3x a day and heavy live brine shrimp with good results. Reintroducing them to the community was 50/50 successful. Some reintegrated and other got picked on again and would decline. 
Purchased kids i would feed heavy and some recovered on their own. I treated the rest with kanaplax each time and many recovered. Those that it did not help I would treat with paracleanse. A few of those would recover then. Some never recovered even with both treatments. 
I hope that helps. Malnutrition causes the curving look in these. Determining the cause - not competing well for food/ bully away from food, bacterial issue or parasitic issue is hard because they all look the same to me.