hair algae eating fish for 20g?

What kind of fish do you have in there? I assume you're raising live plants? If you are, what type of lighting do you have on there? What sort of nurtrient (if any) dosing are you doing? Do you inject CO2?

-Richer

I think amano shrimp might do the trick, not sure. I have the same thing: a 20 gallon with some black hair algae on my dwarf sag. I'm hoping amanos will take it off.

Regardless of what kind of algae eating fish/creature we suggest for you to get, none of them can fight an algae outbreak... unless you also address the problems that are causing the oubreak. The only way to effectly get rid of algae is to stop it from ever happening. Though herbivores generally don't produce as much waste as other fish, they still produce waste... and will add to your bioload. If you can solve your algae problem without the addition of more fish, all the better.

-Richer

There's a small killifish called Jordanella floridae that eats hair algae, and a bunch of small livebearers like limia species. Mollys will too.

Amano is pronounced as it looks... if that doesn't work, try Caridina Japonica. Its not exactly the easiest shrimp to find, but they are cool little buggers. You need a large bunch of them before they'll make any differences in a tank.

However, if you do not solve the source of your algae problem, you will never rid yourself of the hair algae that has established itself in your tank. Seeing how your tank is located near a large window, and undoubtly receives a lot of light... that is most likely your problem. If you can shade your tank from the window that will help. If you cannot do that... then it looks like you may have to resort to converting your plant tank into a hightech one. Look up CO2 injection, and nutrient dosing in the plant forum if that is what you want to do.

HTH
-Richer

Around here amanos are just sold as "algae-eating shrimp".

I have an SAE in a 15, and it enjoys eating hair algae. If you are able to find one small enough (< 3 inches) I'd get one. I've had mine for over a year and it's fat and happy. I'm more concerned about having way too many plants in the tank than the actual dimensions. If you're tank is a 'long' and not a 'high' I'd be even less concerned about it outgrowing it in the short term.