I too need a macro lens and have had difficulty getting shots of my guppies, and I too shoot with a canon DSLR. Though I have no external flash so no black back for me.
Here is what I came up with ...

IMG_5342 by muffywrx, on Flickr
Pretty much the only good photo I've gotten so far that came out clear. Frustrating.
What settings are you using?
Here is what I came up with ...

IMG_5342 by muffywrx, on Flickr
Pretty much the only good photo I've gotten so far that came out clear. Frustrating.
What settings are you using?