Originally Posted by Puffin
64l / 16g. I would like a small Pleco (not a common as I know they get big). or maybe an upside down catfish.
Unfortunately, I gotta tell you that 16 gallons isn't enugh for an angel or the silver shark. Sorry. The silver shark especially is too big. If I was you, I would re-home those 2 guys before adding more fish. Assuming the silver shark is a bala shark, they get to be over a foot long. Also, your angel will likely eat your guppies and fuuture neons as soon as he is big enough.
If you could re-home those 2 fish, then I would probably recommend otos or nerite snails. The plecos that I know of all need more space than that, even the smaller ones. Personally, I am not a huge fan of upside-downs cats. I have some, but I am going to sell them because I never see them. They are nocturnal and just hide all day. The cats wouldn't eat algae anyway.