I think the answers lie with more experienced aquarists than me, Ross...
I just remember the swings I would get in those first few months, and how fickle the tank seemed - I couldn't be cautious enough, and then there was a couple of "wait 6 months for livestock" threads.
So I went pretty slow, I guess, not wanting to upset the "not-quite-balance" of the system. Yes I did at one point lose two week-old fish together that were added together, after I was advised to only add one at a time with a minimum 2 weeks in between... But that was pretty much it for losses, and the only time I can point to where I may have tipped the balance negatively by additions.
The thing is, at 6 or 12 months your tank will be unrecognizable to you, you can see it ripening - it's quite amazing. At a year or more you could maybe get away with intrducing a shoal or so - but I still get real nervous about a new system. Can't help it, after watching mine go through the phases, and then have a green water bloom to top it all off. (Watch your phosphate sources carefully, BTW.
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Don't know if this helps - hope so though.
