Your choice of anemone would be better if you thin in terms of a bulb-tipped nemone (
Entacmea Quadricolor), rather than the
Condylactis spp., if for no other reaon than the aggresive nature of the anemone. Condylactis is not the natural symbiont for most clowns (I do not know of
any that it is the actual natural symbiont, but they may host in a Condy a a surrogate...)
See
http://www.youtube.com/watch?v=hyYW0mr-e7k
and
http://www.wetwebmedia.com/condycompfaq.htm
and
http://journals.cambridge.org/action...ine&aid=201707
You would realisticlly need a bigger tank as Tony has already mentioned, if for no other reason than to handle the nitrogen load that feeding the anemone and a pair of clowns would put on such a small tank. 30USGallons or up for an adult Clownfish pair and a decent sized anemone with good rock filtration to handle the nitrogen load would be much more appropriate. Your tank will also need good intense lighting to sustain the anemone, so a larger tank will help with dealing with the additional need for heat dissipation (best to include a sump with fans to take advantage of evaporative cooling rather than use a chiller).
HTH