With the fish you have at the moment, you are limmited to neons (at least 6), gouramies, small new world (dwarf) cichlids or possibly kribs, smaller rainbowfish. I would avoid discus in your size tank and with some of your fish being quite active. Zebra plecs are more complicated to decide on. Realy they too have rather specific requirements and aren't good at competing for food. I would say you are better off leaving them out in this particular tank. Dedicate a species tank to them with a few peaceful tetras or something if you realy want some.
First, however, decide whether you want to add to your danios and keep in mind that silvertips CAN be nippy. Then get the 3 more x-ray tetras. I would urge you to get at least a couple more danios as well myself. Why not if you like them?
From the new world cichlids, there are several dwarf species that would work in a community. Rams for one are common and a good option. I like bolivians more than the german gold/blue myself - they have more 'cichlid character' IMO. You could also try keyholes which I adore though they aren't realy very colorful. I think, decide on the other fish, sort it all out (get rid of the bala, add the extra x-rays etc) and then ask in the new world cichlids section about which species would work best.
With rainbowfish, colorful/interesting small species are basically the neon blue dwarf rainbows and threadfin rainbows. Neither usualy looks impressive in the LFS tanks so don't be fooled, they color up in time. The dwarfs in particular are stunning blue with red fins and the threadfins develop fins that live up to their name and they have wonderful shades of yellow, silver and blue. Both species are lovely, active fish which would work in your tank as a small school.
When it comes to gouramies, there are several to choose from - if you like dwarfs, I would suggest either banded (colisa fasciata) or thick-lipped (colisa labiosa) gouramies. They are similar to dwarfs but hardier and slightly larger. I just generaly preffer them
. ALternatively, a small colorful gourami is the honey (colisa chuna/sota) and then there's the sparkling and croaking gouramies that would work once you've taken out the bala (a large bala might 'accidentaly' swallow a sparkler...) and provided your tank's going to be pretty peaceful (also applies to the honeys). Other gouramies you may want to consider are pearls 
(my favourite fish! ) or, if you like, a single three-spot. If you go for a three-spot, stick to one as they can be temperamental and you should either keep just one or go for a trio to devide aggression which would take up space. Another possibility would be the moonlight gourami but these would be the largest, though peaceful, at 7" so realy keeping one of these would limmit the space for any other fish.
First, however, decide whether you want to add to your danios and keep in mind that silvertips CAN be nippy. Then get the 3 more x-ray tetras. I would urge you to get at least a couple more danios as well myself. Why not if you like them?
From the new world cichlids, there are several dwarf species that would work in a community. Rams for one are common and a good option. I like bolivians more than the german gold/blue myself - they have more 'cichlid character' IMO. You could also try keyholes which I adore though they aren't realy very colorful. I think, decide on the other fish, sort it all out (get rid of the bala, add the extra x-rays etc) and then ask in the new world cichlids section about which species would work best.
With rainbowfish, colorful/interesting small species are basically the neon blue dwarf rainbows and threadfin rainbows. Neither usualy looks impressive in the LFS tanks so don't be fooled, they color up in time. The dwarfs in particular are stunning blue with red fins and the threadfins develop fins that live up to their name and they have wonderful shades of yellow, silver and blue. Both species are lovely, active fish which would work in your tank as a small school.
When it comes to gouramies, there are several to choose from - if you like dwarfs, I would suggest either banded (colisa fasciata) or thick-lipped (colisa labiosa) gouramies. They are similar to dwarfs but hardier and slightly larger. I just generaly preffer them
. ALternatively, a small colorful gourami is the honey (colisa chuna/sota) and then there's the sparkling and croaking gouramies that would work once you've taken out the bala (a large bala might 'accidentaly' swallow a sparkler...) and provided your tank's going to be pretty peaceful (also applies to the honeys). Other gouramies you may want to consider are pearls (my favourite fish! ) or, if you like, a single three-spot. If you go for a three-spot, stick to one as they can be temperamental and you should either keep just one or go for a trio to devide aggression which would take up space. Another possibility would be the moonlight gourami but these would be the largest, though peaceful, at 7" so realy keeping one of these would limmit the space for any other fish.
