Find another fishkeeper, or donate to your LFS.
No tetras belong in a 5.5G tank, long term. And all tetras need to be in groups of 6, more preferably.
Wow, a newword going down in forum history
Try to clean the ilter a bit or add more placed for bacteria to live ike rocks. Diatoms or brown algae can be remved by a small cloth or just an algae snaaprrf .
My spelling kight be bad im on a phone :0
Get a scraper for such ansmall tank, and use it to scrape the qlgse off and turk filter off whne you are dign it. Or it will spreqd and poor old ramshorn will not br able to eat so much algae (yes rams do help)
Try balanxing the tank, with more plants or things to sap up the energy so it is jot used for algers