My Oscar near the same age and size lost appetite for food he loved and seemed to have stopped growing early. Also(I don't know if you have introduced anything that should spread infection, but mine also had several fungal infections with no new living creatures added(food or pets), and never having been stressed, all of which seemed to heal fully. Then I saw a white string hanging out of his anus which I learned is a tell tale sign of an intestinal parasite. This was maybe two months ago. So I treated him with levamisol in the form of discomed and he didn't seem to get better, not that he was acting as if he were in pain, but his appetite didn't increase much if any so after a week of no drugs I treated him with metronazidole, both of which I administered by soaking his food, and I also treated his only tankmate which didn't show any symptoms but I thought better safe than sorry though it seems like its unlikely to have been transmitted through the water. Anyway his appetite is much improved and he may be growing again, hard to say for sure, but his appetite isn't as strong as it seemed to be at one point. Also when he really seemed to lose his appetite was shortly after i moved him up to 5 smaller feedings a day(I was very careful to never overfeed him especially then), apparently they can be carrying the parasite and not show symptoms until they're being really well fed. Because of the facts that his appetite may not be fully back, I saw some posts or maybe it was other material that made it seem like intestinal parasites are very persistent, and the drugs when administered correctly seem pretty safe(some people say metronazidole is very hard to overdose, though I wouldn't f--k around pushing it), I'm going to give him that same course of treatment again soon. Sorry for the lack of paragraphs and any spelling erros here it's way past bedtime, I'm trying to finish Far Cry
, its like a drug too .
You might try a week of metro soaked food, starve him for a day first just don't look at his big sad eyes and only give him food thats soaked in metro for that week(to make sure he eats it) . You can get it cheap at Drsfostersmith, I followed the directions and did the garlic guard and focus thing with it, though those last two may be hype. I don't know what kind of food you give him but if you use pellets you can put like two tablespoons of garlic guard and 2 measures of focus and one measure of metro and stir it up and soak your pellets in it, then feed them to him while they're still wet or moist(seachem told me for focus to bind drugs to food it has to stay wet or moist(which is what makes me think hype btw, I figured wtf though)) then if you want to soak more and put them in some tupperware or something in the fridge they'll stay moist, and you can save the mixture. They told me to soak the pellets for 10 minutes but they totally start breaking down long before then, I just keep the mix stirred really well and get them submerged in it for maybe a minute.
