I own two male bettas, separate 3L tanks for nine months.
One of them died five hours ago from hidropsy. I noticed him getting bulky one day, talked to a friend of mine that breeds bettas on the other day (yesterday) and he advised me to euthanize my fish. I did not, just leaving him alone, and he passed in less than 30 hours.
This other fish I'm left with has always been treated exactly the same, is kept on the same water, is fed the same food at the same time. I have been noticing he hasn't been very active. Eats fine (the other one didn't for a day before he started bulking), but doesn't swim around. Stays on top of the water always on the left side. I tried exposing him to a mirror to see his reaction and.. there was none for at least 3 minutes, then he just moved to the other side of the aquarium. I chased him with the mirror, he took a while again to react, just going back to where he was.
I'm really worried I might lose this other fish, but I'm not an expert on the subject or anything. I just kept these two. The only fish supplies I have are the water conditioner and an anti-protozoary anti-bacteria medicine I once bought to fight off fin rot. The fish is fed with pellets, I have two different brands.
I have read he could just be constipated, but I still don't know what course of action I should take. The fish is a year old, and I've been told by my friend he has poor genetics (i bought him at a pet store for a dollar and a half)... could he just be getting old?