laying at bottom and acting lethargic

[labloverl]

There's nothing on him. His fins aren't clamped, but he does look ever so slightly bloated. I can hardly even tell.

[BETTACHKALOVE]

well it make the difference for the treatment though. If it flukes which might be not visible to naked eye then you need aquarium salt.
If he is bloated he might have internal parasites. And especially you saying that he had it a month ago. How you know you got rid of them. What color and shape is his poop? With internal parasites fish will be bloated, and poop will be white,clear stringy wormy shape.
So if he bloated - epsom salt.
Is he bloated because he didn't poop for a few days or it can be internal parasites inside.
Do not share anything between him and other fish.

[labloverl]

I don't know. :( When he had the internal parasites before, he just seemed "off" one day. He wasn't his usual self, and he was clearly bloated. Not a lot, but I could tell! With epsom salt, the bloating went down, and worms started coming out of his side. The other fish were never affected. I feel safer putting him in epsom salt tonight as he did well with it. Can I leave him in the cup and continue floating him?

[BETTACHKALOVE]

Yes you can.
If he had internal parasites, eplsom salt will help to purge the parasites out, but it will not treat it. So if you didn't use medications i would think he had some left and now he still have them.
Did you see his poop recently?
You can leave him in the cup floating it fine. Use 3tsp/gall of the epsom salt make daily changes.
Can you buy medications for internal parasites?
Make sure he is isolated from other bettas

[BETTACHKALOVE]

i have antiparasitic medications that i can mail to you but i can do it only on monday:(
If he has internal parasite it better if fish is eating so if he eats feed him. They pass them with poop

[labloverl]

Thank you! I will put him in epsom salt tonight to see if I can get him feeling better. I do have anitparasitic meds to use. :) He has pooped in the cup, but it has all come apart, so it's hard to know what it actually looked like before.

[BETTACHKALOVE]

Do 100% water changes not 50% . And add 3tsp/gall of epsom salt. And if you can check for the poo again after you will do 100% water changes. Actually if his poo all apart can you tell what color it is? If it brown it fine if it white or clear parts then it parasites.
And watch his bloating if he will get more bloated and pooped, and poo white or clear i would assume that it really internal parasites. And if it is you need to use medications combined with epsom salt. And again it better if he eats.

[labloverl]

The poop was some color between white and brown. I know that's not helpful, but :/. He's not eating tonight. He can hold himself up in the water for a short time, and then he has to lay back down.

[BETTACHKALOVE]

You know i would really use medications today even . The reason why because since he is bloated and you see white poop partially i wold use medications and 3tsp/gall epsom salt with daily water changes. You can loose him i think so why not try. With internal parasites they deteriorate very fast and die very fast so i would put medications.
And when you do 100% water changes i am sure you know about acclamations just redoes require dose of the medications. Not sure what is the instructions. I know that on some medication it just one tablet for 48 hrs. So for example you are going to change the water and with every change just add one tablet. And take time to acclimate.

[BETTACHKALOVE]

Very sorry. But if you ever see that your fish has internal parasites always treat with medications. Epsom salt is helps a lot but don't treat :(
Good luck give us update. I think be ready for worse and hope for the best. And check on the bettas if any was in the same tank with him or if you share anything between them.
Also when you have filter make sure you rinse it regularly.
Sorry for saying it but if he dies make sure you disinfect the tank completely before you put another betta in there.