agreed. Just use an algae scrubber on it. Soap, if it gets back in the water, will stress out your fish at the least, artificial scents and such. At worst, it could form a coating over your fish's gills (not entirely sure about this) but it is NEVER advised to introduce foreign chemicals into your tank unless they are proscibed in the trade (medicines, de-chlorinators)
If your having a build up of hard water or something that is effecting the beauty of the tank, you can use vinegar (obviously not while the fish is in it!
Beneficial bacteria are great, but you probably don't have enough in that bowl to make a difference. BUt here is a tip, algae needs nutrients to grow, and nutrients usually come from your fish! in a 2 gallon bowl you should be changing a large amount of water every week, or maybe a cup of water every day. THis should reduce the nutrient load in your tank and help you control the algae.
Do you have gravel in the tank? if you do, and you want to slow the return of your algae, you can nuke it in the microwave (as long as no metal is present.) this will sterilize it, you'll need to wait for it to cool before re-adding it of course. and wash it again. This will kill beneficial bacteria as well though.
FInally.. an important question... what color is the algae? sometimes, just giving it less light will work, unless it is a bacterial growth some equate to algae but is not... brown and other colors should be aggressively fought, while green, is ugly, it gives your fish a garden salad to nibble on every now and again.