Reret, we are not here to do the research for you. You are very obviously not doing any before you ask the questions. As a bare minimum, you should be Googling (or whatever you use) for the species you are asking about and reading the first 10 results (not only one or two), then coming back here and asking real questions.
You will not be adding anything before your aquarium is cycled, which will take 6-10 weeks with a fish-in cycle. Before you look for new species, you need to know*everything* about cycling the filter, this will take you 1-3 hours of reading and looking at cycle logs.
You obviously also have problems with diseases, so you need to research these: this will take you 1-2 days.
And with algae: this will take you another 1-2 days.
Next, you need to research the species you already have: another 1-2 days.
Only after that should you start even thinking about researching new species.
Glass cats are not suitable because your tank is too small and they are very shy. Corys would depend on the species, although I would personally not put them in a tank that small.
Here's a free hint: tetras, barbs, rasboras, Corys, mid-water cats and the like are all schooling fish. This means that they need to be kept in groups of at least 6 per species and ideally 10-15+ per species. You can read more about it here: http

/aquariumadventure.wordpress.com/2011/09/07/deciding-on-fish-numbers/