I, too, need to control algae in my tank. It's a six-gallon Eclipse. Right now, it houses Candi the Betta and one dwarf Habrosus Cory. (The other two Cories only lasted two to three weeks and died suddenly and mysteriously.) I realize Cories appreciate tankmates, but this cute little guy seems fine as far as I can tell, and I've kept him for about three months. He even mistakes Candi for a rock or something and has "sat" on her a few times. When she moved and he realized what he was "hugging" with his pectoral fin, he got out of the way quickly.
He looked like "Yikes!" Otherwise, he's calm around Candi even when she tries to steal his food, and she's kind to him.
My dilemma is that I'm very hesitant to get two more dwarf Cories. First, I'm not sure the present little guy would bond with them, and I'm also concerned about introducing disease into Candi's tank. I have a 2-1/2 gallon quarantine tank I could use, but it's not cycled. I would cycle it before buying the little guys, but it still seems kind of risky and very time-consuming.
Meanwhile, I would like some housekeeping help for the algae. I don't know why it's as bad as it is. The tank has live plants and generally the nitrates are 15
PPM or below. I know, I know, I should keep them below 10 ppm, but that's how it is.
Since I have such limited space, I've considered getting a couple of tiny Otos. According to liveaquaria.com, the following species reach only 1.3" to 1.4":
mariae, 1.4"
macrospilus, 1.3"
vittatus 1.3"
I realize I'd have to quarantine Otos just like I would two new Cories, but at least I'd have some housekeeping help. "Daryl" doesn't appear to be much help. He/she doesn't do windows, like cleaning algae, but perhaps he/she helps clean the toilet. (Candi's poop in the substrate?)
Now you've got me interested in shrimp. I know nothing about them. Are they as industrious as Otos? How hardy are they? Do they have any communicable diseases that could affect Candi or her Cory?
BTW, the original three Cories were named Larry, Daryl and Daryl. That's from the old Bob Newhart show. I'm not sure which one is left, but I'm pretty sure it's one of the Daryls. He (actually probably a she) is adorable, even though no fish can relate to us humans the way a Betta can.