He's skinny, pale and sluggish. Should I assume an internal bacteria infection?.

I hate to say it, but I've been running late on water changes so I assume that contributed. Nothing else bad/stressful seems to have happened in that tank.
I was hoping a good water change would get him going again and instead he starts to rest on the bottom so I think I need to take him out and treat him today.

He lives in a 20 gal high with his mate and about six baby plecos. The other fish seem healthy.

Sorry to hear your fish is sick. Unfortunately it is very difficult to make a diagnosis from a distance. Its possible that he has a bacterial infection or he could have parasites (worms).

The most important advice I can give you is to move the sick fish out from the group tanks to an isolation tank. The others may be fine now but if the problem is infectious they could be vulnerable.

It is not a good idea to try to treat with antibiotics while the fish is in the group tank either. In fact, it isn't a good idea to treat with antibiotics unless you know you are dealing with a susceptible bacterium. In this case I'd be inclined to try treating the fish in a small tank with a worm medicine like fubendazole. You won't find the latter in pet stores etc. but if you know any local killie enthusiasts one of them might have it.

Barry Cooper

Another bad thing is I was about to re-home most of these baby plecos and keep two.
Now in good conscience I don't think I can re-home them since they might be carrying a disease.

I have some parasite meds, but probably not that kind.
I only know one local fish club person and they don't keep any killifish.

Well, as I said, get that sick fish out of the tank and isolate it. Then give the others a period of observation to make sure nobody else gets sick. Realistically, you may lose the australe but it would be nice to make sure the others are OK.

You can put the australe in a small container like a gallon jar. Treat it with the antiparasitic meds. It won't hurt. I'd be reluctant to use antibiotics. Your chances of success are not good and there is a risk of producing resistant bugs.

I admire your ethical approach of not distributing the plecos until you're sure they are not affected.

Barry

He's in a small cup with a lip on top. I'm running into work-time( I go to a nursing home to massage someones' feet) so I hope he's OK there for about an 1.5 hours.

I was cleaning a small tank up with bleach to use as a sick tank for him and ran out of time.

I'm sure the fish will be fine for that short period of time unless his ailment gets to him.

We can become attached to our fish as pets and it's not enjoyable to see them sicken and, eventually, die. However, it's an aspect of the hobby one has to get used to. The fish have relatively short lives so we are going to lose them periodically. I hope, however, that your guy recovers from this present problem.

BC

I put him in a about a one gal half filled two gal tank and treated him with some parasite meds.
Today he's not sitting on the bottom so I hope he's getting better.

The difficult part is I've been dealing with a lot of other issues and plan to leave in less then a week on vacation, so it's been hard to give sick fish proper care.
I hate having sick fish on hand when I leave since my vacation/leaving setup is automatic feeders. Not that most fish sitters could handle treating a sick fish anyhow.

I do get attached to my fish, though it really depends on how long I've had them.

Oh and I've started naming my fish after my porfolio/story chars so I named the killifish couple; Chaz and Kytene (pronounced Kite-knee). Chaz is the male and Kytene is the female.

Sadly he died during the night. Maybe he was too sick or maybe didn't actually have parasite problems.

I'm sorry to hear that. Don't give up. All of us hobbyists lose fish occasionally. It is disappointing but it is something we have to come to accept.

Barry Cooper