Welcome to the forum, there's a lot of help here. As mentioned a picture would help identify your fish, but I think you're fine for a few months. I would probably try to get a 190l, 50 gal or bigger long term though. As for the pellets, what brand are they? It's common for fish to be picky when switching foods, but keep trying, don't give them anything else for a few days while trying the pellets and they may take them when they get hungry. Even if they refuse the pellets they'll be fine without eating for a couple of days. It sounds like you're doing a lot right. This can be a confusing hobby when you first get started but it sounds like you've learned a lot already and are putting in the work to keep them healthy. Good for you! You also may consider some type of small bottom feeder like a bristlenose pleco or rubber lip pleco. There's many that would quickly outgrow your tank but these 2 kinds stay small and can help with algae, but also will eat the food that escapes .