Algae is almost never harmful for fish, so its not going to be a worry with your danios I don't think. I've never heard specifically of "yellow algae" but brown algae that sometimes looks darker brown and sometime more rust colored, almost orangy reddish even, is very common.
If you search this forum, there are threads on algae and somewhere in them you will find links to web pages that have pictures that help you identify specific types of algae. I think I remember that maybe Aaron North's sig might have such a link but i'm not sure. At any rate there are a bunch of types.
Presuming you want to learn some magic way to get rid of this algae I will just say that algae is a much trickier topic than one usually initially thinks and few answers are necessarily definitive. I would comment that there are probably there are more aquarists than you would think that are just diligent about scrubbing algae off using a small sponge or other device just prior to their weekly gravel-clean-water-change!
~~waterdrop~~
what's and why has my 75lt tropical tank got yellow algae (only on the back seams) - 4 zebra danios seem fine - had tank approx 6 weeks now.
