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Not sure where this technically belongs... Being as the BGA is a bacteria and not a plant, and I would consider it a parasite, this is where I landed.
Have a 35g with a 10g sump and 1 3in or so loach, 3 Honduran Red Points and 1 tiny earth eater. There are a few plants, lots of sand and one pretty potent light. It is HEAVILY affected with BGA. Obviously cleaning didn't help much, did a total break down of the tank and washed everything, even the plants. It's back. What's the next step? Time isn't a big concern for cleaning. Should I dose with an anti bacterial? Total blackout? Wash with vinegar and bleach dip the plants/decorations and equipment? I don't really care about difficulty, just want it to be gone, preferably forever:)
Also wondering if this stuff can hitch a ride on fish. Also what causes it, flow in the tank is around 200gph, doesn't mean there are not dead spots though...

Erithmyacin will kill it but it would take a good bit of it and using a medicine is not always the best bet. As a last shot though, it does work.

How long do you leave the light on each day? Reducing it might help some, and oto's or bushynose may be beneficial also. Any chance you're overfeeding? Denny

Cyanobacteria or "blue green algae" is the same basic thing as the reddish slime algae you see in saltwater tanks. Typically this will show up in tanks that have an excess waste and lack of water movement. I've had several tanks with this and have had little reason I could pinpoint being the cause. Identical tanks sitting side-by side with the same gravel, under the same strip-light (on a rack) with the same water, same filtration, same temperature, same types of fish, same food, everything and one tank would get it, the other wouldn't. I could do washes and water changes till I was blue in the face but it didn't seem to make a difference. Erethromycin (or EM Tabs) will work along with water changes but be careful not to overdose because it is an antibacterial and can wipe out your biological bacteria as well.

a tip I picked up recently from a plant guy you might try (I havn't had a chance to try it myself). He brought up that plants were a higher level organism and that if you cycle your lights on and off during the day (couple hours on, half hour off, couple hours on, hour off, etc..) that the plants are able to start using the light much faster than the algae can so by the time the algae gets geared up to utilize the light, it goes off and they have to start over and can't recover like the plants can. sounds reasonable, might be worth a shot...

Most of the tanks I've had issues with I ended up just completely tearing down and replacing with another tank (I have lots of empties) and then letting all the components dry out completely before re-using. I do not see how a fish could carry cyanobacteria although if you stir it up in the water it definitely could migrate there. I've never had an issue with it spreading from tank to tank though, some sort of imbalance seems to start it off.. Kyle

Blue-green algae is a tough problem to deal with. Weak water current, insufficient filtration, overfeeding, etc. have been blamed, but I've seen it happen in tanks where everything appeared right. Cichlids that dig and move gravel can bury nutrients, which might contribute. If extra gravel vacuuming and water changes don't make it go away, just turn off the lights and dose the tank with erythromycin (Maracyn, E.M Tabs, etc.) for about three days. Follow the instructions for using the medication to treat fish disease. This has always worked for me.

I had heard rumor that hornwort kills cyanobacteria. I had a tank that had lots of hornwort in it which suddenly all became covered in the blue-green algae. The hornwort was there before the algae! So I completely discounted the rumor. Then the blue-green algae got so thick that it killed much of the hornwort. So I doubly discounted the rumor. Then, two days later, the algae spontaneously disappeared. What the...!? So, maybe, DYING hornwort kills blue-green algae. I don't know. I've never had opportunity to witness this again. Maybe you could mash up some hornwort in the tank and see if it does anything. Then report the results!

Well thanks for all the advice. It is my wife's tank, since she isn't showing too much concern, I haven't either.
Medication will hospefully be our last attempt.
The light used to be on around 12hrs a day. Since I've posted the lights have been a total of about 11 minutes. Woke up late and turned everybody's lights on, then realized that light shoudldnt be on. Turned it off. The lack of light has caused quite a ruckus in the BGA community. They've mostly died off, except for the few who have migrated to the west side of the tank. It doesn't receive light for long, from the sun, but it is powerful light.
All of the plants in her tank are lowlight friendly, they seem to be doing fine with intermittent light from the overhead fixture for the room. The BGA needs more:) So I don't plan to try the on off remedy.
April despises hornwort. She likes rooted, broad leaf plants. Overfeeding is highly unlikely. I am stingy with the food, and filtration is excessive:-) hopefully I can find a less intense bulb lying around, and I may modify the circulation to increase flow. Thanks a bunch folks!