Where am I in the Cycle?

[StickmanInDC]

Hey folks! After six months of reseraching, acquiring, building, and setting up, I'm finally starting my first reef tank - a 75G with 20G sump. The tank seems to be cycling rather quickly, so I'm a bit suspicious and thought I'd get an opinion on where to go from here...

12/4 - Filled tank with RO/DI water, added salt, heater & powerhead
12/5 - Salinity 1.026
12/12 - Added 75lbs of cured live rock shipped in from Premium Aquatics
12/13 - Added 60 lbs of dry Caribsea sand (mix of Fiji Pink & Special Grade Reef)
12/14 - Ammonia 0.5 - added a raw cocktail shrimp to kick off the cycle
12/16 - Ammonia 0.75
12/19 - Ammonia 0.5, Nitrites 2, Nitrates 30
12/21 - Ammonia 0, Nitrites .5, Nitrates 10 - cocktail shrimp is halfway gone

I'm surprised that the ammonia and nitrites are dropping so quickly - am I experiencing a really quick cycle due to the large amount of cured live rock (color me skeptical), or have I not actually started to cycle yet? (or is my Red Sea test kit totally misleading me?) Powerheads and return pump are on, skimmer is off. I'm still finishing up my DIY LED lighting rig so haven't been able to run lights yet but will hopefully get them on in the next few days.

Any thoughts? Thanks in advance for the advice!

[brcb7tuner]

When I upgraded tanks I only waited about two weeks and was adding some of my hardier corals and everything else within one month and everything did fine. I would just start adding things slowly and keep an eye on your parameters.

[MARINECRITTERS]

I would still wait a few more weeks. Your tank is cycling correctly, I see nothing wrong.
You do still have nitrite which is toxic to the fish, once the nitrite is completely gone, wait a week or so ( make sure there is no ammonia spike ), then you can probably add your first fish ( only one, bacteria populations are still quite weak in a new tank ).
Why are you running a HOB filter? With time they will become a nitrate factory.

[cheezybuda]

That doesn't seem like a huge ammonia spike, but maybe your cured rock had enough bacteria to handle the shrimp.

Btw, I would recommend breaded popcorn shrimp next time....the bacteria like the crunchy coating ;)

[StickmanInDC]

Thanks for the advice - sounds like I'm on the right track! I'm setting up a QT in parallel with the DT, so it will be at least a month before I add a fish to the main tank, but if the nitrites comes down to zero and stay I'll at least add a clean-up crew and ghost-feed in the meantime...

I ran the HOB filter after I added the sand to clear up the cloudiness and just haven't taken it off the side of the tank yet. I washed the sand as best I could but it still made a bit of a mess - the HOB filter cleared it up in about 12 hours.