i'd take out about half. it'll regrow fast enough. and for the record, IME the whole caulerpa going asexual thing is a little overplayed. it happened to me once(because i didn't thin often enough), but i saw it in the morning, put a canister with fresh carbon on the tank, and started running the RO for a 1/4 waterchange, did the WC in the afternoon. that evening we had a party. noone even suspected that anything had been wrong. water was clear, NO losses. and this was in a crowded mixed reef. so, you do hear stories of disasters, but i think it's a bit overblown. that is to say, don't go and spend the holidays picking all the caulerpa out of your chaeto with tweezers or anything.