Ok, i have added a few corals now and a couple of fish, going along nicely, did have a bit of a worry before adding the fish as the nitrate went through the roof, however we managed to get it down enough to add fish and coral.
Although we seem to have managed to work out how to alter the tests if needed, our LFS never explained anything about the tests when i bought the tank, especially how to alter if anything is wrong. with our nitrate going through the roof we just kept doing a 5% water change and that improved things nicely.
Crab update, we bought a trap, but still have not managed to catch him, the snails are clever enough to get back out of the trap!!