Against hair algae, i personally found Amano shrimp worked best for me... but i do agree with others when they say, try not to overdose on the Excel (liquid Co2) since i've lost some shrimp to overdosing in the past...
Also, if you want to use it against the hair algae alone, one way you can do it is to get a syringe and measure out the correct amount for your tank size, and then using the syringe, release the excel directly above the hair algae (over a few days using the correct dosage) and withing about a week or so, most of the areas you spray should disappear...