To clear up the mystery:
4kg of the live rock came from a previous marine tank that had been going for 6 months (along with the damsels and some inverts).
26kg of the live rock came from a previous marine tank that had been going for 2 years.
All the live rock had/has good healthy coraline growth (the purple stuff) and has lots of little fans, etc. all over it.
The tank was run with the internal filter from the 6 month old tank for 3 weeks to help the Eheim Mech in the filter chamber seed.
Nothing was added for the first 3 weeks to allow the tank to settle and die-off to finish and only when the water parameters were perfect did I add more inverts and some soft corals.
I took a water sample to my LFS who tested it and had a look at it under a microscope (he's nothing if not thorough) and even he was surprised at the maturity of the tank and the fact that I have a healthy colony of copepods (tiny white wriggly things that live in the sand and rock) and other organisms. The tank is nowhere near the level of maturity needed to add more fish but it is stable enough to add soft corals and a few inverts.
In many ways a marine tank is like a tropical in the way that it can be 'cycled' in a shorter time using existing filter medium/substrate (in this case the live rock and internal filter).
It's amazing to watch as everytime you look at the live rock there's something new growing on it and I would recommend anyone to have a go at setting a marine tank up if they have the resources, they are so cool to watch
