It should take a few weeks for all the sand to become "live" and yes you can seed your dead rock with live rock and it will all become live in time. The amount of time it takes varries from tank to tank but it doesn't take to long and if your starting a new tank you shouldn't be in a rush anyway
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Kathy and others will chime in
Lenny has it right
All depends on the size of the tank - the smaller the tank, the faster it will all become live, also consider the depth of the sandbed. Of course, the more live sand you add, the faster it will happen. Bacteria in a sandbed can multiple every 2 days..amazingly fast!!
Someone mentioned 'dead' sand...if you are thinking about using dead sand (as opposed to new unlive sand), I'd be very careful about rinsing the heck out of it first to get all of the crud out. The other chance you take with dead sand is not knowing how much phosphates it may have absorbed in it's prior home (that will leach back into youir tank, very possibly causing algae issues). Personally, I'd pitch it and get new sand.
Rock - takes longer, but not by much, pre-curing it before you put it in the tank is always a good idea if you have the time.
Base rock is also a good option (dry rock, uncured, and has no pests, no phosphates, no color - it's white/beige & cheaper than most other rock)
Going to mention one other thing - coralline....you can also 'seed' coralline by scraping bits of it off a rock with coralline the color you like (yes, it comes in different colors
) It can be red, orange-ish, pink, and a bunch of shades of purple. As long as you have stable Ca/alk/Mg - at the correct levels - you scrape some off the chosen rock and it will seed onto your other rock. It is a slow process..good flow also helps here, but well worth it in the end. Some of the colors are stunning and it does set the backdrop for all of your corals
Purple Up can easily throw your parameters out of whack..you don't want go there...
Going to quote what Lenny said above and it applies to all I said:
The amount of time it takes varries from tank to tank but it doesn't take to long and if your starting a new tank you shouldn't be in a rush anyway
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Oh, so very true!!!