I recommend a few otocinclus. They are shrimp safe algae eaters, and stay quite small. Only problem is they prefer to be in groups (recommendation is 6 as a minimum), so it would eliminate your hopeful addition of more tetras. Petsmart and Petco carry them, as do all of my LFS. More info on them:
Other thing of note, they are almost all wild caught, and between shipping and being kept in clean tanks at the stores (because let's face it, no store wants an algae filled tank) they are normally starving to death when you get them. Of the 8 I bought, I have 2 remaining (other 6 died within a week), and have had those 2 for about a year now, living well in my 75. My LFS got a shipment in today, and as soon as I can make it out, I'm getting a few more. From what I have read online, people experience about a 50% loss within the first month. I wouldn't overpopulate your tank expecting it, though.
Another option would be a mystery snail. Of note with these, they get bigger than I originally thought, and over-stocked my tank (I got 20, and have had to spread them out in different tanks because they poop more than a pleco). If they don't like the extra food you need to feed them, they will eat plants.
Also of note, the past week I have typed many different responses to many different people, and never clicked "Post", both here and on facebook, and I am very sorry for the delay on sending you this.