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I have had very good luck with mine. There are two in my 55gal with boesemani rainbows, Endler's livebearers (including fry, of course), serpae tetras, white clouds, cardinal tetras, etc., etc. and they have always been wonderfully behaved. I used to have three in there but I moved one over to my 37gal that will eventually house A. calvus and currently houses 7 praecox rainbows, because there was a severe outbreak of hair algae. In a day this single flag fish had compeltely eliminated the tank of the scourge. He does not bother the rainbows, and schools with them. I think they are outstanding algae eaters.
There was a discussion recently about there being two types of fish commonly sold as flag fish, one being more aggressive than the other - anyone remember?