"Bob" wrote in message
...
The foam is most likely disolved organic compounds (DOCs). You can buy
products to help remove them, or you could do a couple of water changes to
dilute it a little bit. On the other hand, it could be the fish spawning,
but since you just added them, I don't think that's it.

Hope this helps,
Bob


Bob's right. The waterfall forces minute bubbles of air under the surface,
the DOC's cling to these bubbles and are brought up to the surface where the
bubbles then burst leaving the waste on the surface as a scum or foam.
Marine aquarium owners will have a device that recreates this process called
a 'Protein Skimmer' as it is an efficient way of removing waste from the
water - you simply remove the foam! It really shouldn't happen in your pond
however if everything is ok.