Sorry I didn't realise you had posted both! They don't appear to be sick and still seem quite active. I cut down their food a while ago thinking they were just obese, but it didn't really make much difference (except they got no bigger). I feed them once a day and only what they consume within a couple of minutes. If I can get a photo I'll try and upload it tomorrow so you can see.
You're stunting their growth with the small space. As tizer said, they're going to suffer from deformities, they will "grow to the size of the tank" but their organs grow past the size of their bodies. Their life will be shortened, and they'll die very painfully.
I don't even know what you'd put in a 13 liter tank, even a betta could use a bit more space than that.
Depending on what your "algae" eaters are, they could either stay a good size at 1-2 inches (otoclincus) or they can get up to 8 inches long (algae eaters of chinese, gold, regular, siamese) or even up to 2 feet (common pleco)
Angelfish grow throughout their entire lifespan if the space allows it, usually they get up to 6 inches long, even more inches from anal to dorsal fin, so they need a nice tall tank with about 30 inches of length to it.
As said by tizer again, silver dollars get 6 inches or more of size in diameter.
Tiger barbs themselves are pretty bulky despite staying in the 2.5 inch range, they're also active fish, and very nippy when put in small groups. I'd advise nothing less than 20 gallons.
Rams are also pretty bulky fish, although they stay in the 3-4 inch range, and should have about 30 inches of space.
Danios are very active schooling fish, and although they're very small, they enjoy a lot of room for a lot of swimming, some people are advising at least 4 feet of length for them to zip around.
Why I was asking about the tiger barbs is because it's possible, as said, that the cramped space is causing deformity, and the lack of eating can also be a sign of constipation or dropsy. I highly doubt your tiger barbs are breeding, though.