I wouldn't, really. 5.5 gallons is too small for Glo fish, tetras, and a cory cat alone. (BTW, cories need to be in groups of at least three!) If you upgraded to a 10g, you could easily do that, and get the cory cat some friends so he is happier!
i believe most people will tell you that is an overstocked tank, were not trying to sound rude, but, if you want the fish to thrive, they will need a bigger tank
Do you ever think the one that died did so because the tank was over stocked? It all depends if you want your fish to just live or do you want them to be happy and healthy?
not to be rude, but I'm shocked you kept 3 tetras, 2 glow fish, ad a cory cat in a 2.5g tank!!
OK, let's play the Rule of Thumb game. :) An inch of fish per gallon.
3 tetras: 1 inch each= 3g taken up
2 glowfish: 1 inch each=2g taken up
1 cory cat: 2 inches= 2g taken up. BUT, you need your Cory cats to have friends! So, yes, it's overstocked, and that cory cat is stressed.