Since this is the first time I have ever looked at all of the information on UV Sterilizers for small tanks this is what I have found: They won't work on your size of tanks. Any tank less than 40 gallons is probably going to require a chiller. I can't find anything that can be useful for you using this method. Well...The idea was there, anyway.
Okay..This is what I am researching right now. The possibility of using a UV Sterilizer Lamp or something similar. This also caused me to start taking a look at how people treat outdoor ponds for all algae without harming fish/filter media colonies.
This is what I was looking for and couldn't find based upon the same principle as an In-Line Sterilizer: A hand held sterilizer or a stand alone out of the tank lamp sterilizer. The reason that I was looking at algae control in ponds is because of the larger size of ponds (rather than tanks). I was looking for something for you to add to your tank to get rid of it naturally. Well, I found what I was looking for and it won't work in anything less than 50 gallons. I am sorry. I have seen that gelatinous mess on a very large scale. I didn't want to deal with it.
Blue-Green Algae reminds me of a stalker boyfriend. It's always lurking. No matter how much you want it to go away, it keeps coming back. You're never quite sure that if you let your guard down, it won't sneak up on you. Will you be able to fight it off, or if it will overtake you?
Geez, no wonder I find this algae deeply disturbing... :\
Since I am so dogmatic about trying to find an answer and/or solution to this person's problem because I have seen the results of this algae. I am going to turn this information over to Oldfishlady and the person whom has the tank; As, I have never used this method and don't know anyone that has. I have been reading several websites and forums today and I am seeing that people are using Hydrogen Peroxide to spot treat tanks. So, there it is: Hydrogen Peroxide, this information might be worth pursuing or not. If Oldfishlady and the person whom has this tank feels this is worth pursuing, the dosages are available as per size of tank. If anyone wants links to the sites, I can provide those.