Hi cheerfulmelody, and welcome to Tropical Fish Keeping forum.
Now to your issues. First, we have a section here called "Tropical Fish Profiles" that you can access via the second tab from the left in the blue bar across the top. In posts, if the name of a fish or plant is written exactly as it appears in our profile, it will be shaded so you can quickly see that fish/plant profile by clicking on the shaded name.
If the "algae" eaters are Otocinclus, they will be fine; check our profile for Oto Catfish for more info on this species and photos. If the fish is actually a Chinese Algae Eater, commonly sold as "algae" eaters, return them; as noted in the profile they are not suitable fish (and as they grow they eat less algae anyway).
A 20g is too small for angelfish, unless you had a breeding pair. As noted in the profile, they should be in a group as they are shoaling fish, and that means a 4-foot tank. Pterophyllum scalare is the species of the commonly-available angelfish.
Dwarf gourami have issues, again see the profile; I would suggest Honey Gourami are preferable in a 20g, note the info on numbers, etc. in their profile. Tankmates have to be carefully selected as it mentions.
Many fish, like the loaches, are shoaling fish which means to be healthy they need to be in a group; this must be considered when thinking about each fish, as it means adding several fish to the aquarium. And a 20g, while larger than the 10g, is still not very large.
Hope this helps a bit; ask away, we are all here to help out when we can.