Thanks guys, from the HHFAQ description I would say they are amphipods- may be wrong, but they are definitely not cirolanid isopods...
My tiny occi clowns are loving them and are looking incredibly healthy and colourful, and spend all the time hunting them in the water column. Their arrival has coincided with the appearance of some hair algae in the tank, sump and fuge so it would seem to make sense...now to get them into the main tank.......(the fuge drains thru 3" of live sand into the equiptment chamber, dont see them surviving the sand and return pump, not to mention the skimmer!)