Silly Cycling Question

[corey.nolta]

Long story short, I was in the middle of a rebuild that was put on hold due to a kitchen remodel. I got it all set up and filled 90% with water (up to the overflow bulk heads, as plumbing wasn't finished) to make sure there were no leaks from moving it around quite a bit. And then had to stop due to the remodel. This was a month ago. So the sand and rock work has been submerged in fresh ro/di water (no salt) since. I got curious and was wondering if this past month the water had done any sort of cycling. So I tested it and was surprised with the results and wanted to verify.
Ammonia was 0. Nitrite was 0. Nitrate was ~10.

Could there have already been a cycle? There was no heater and very little water movement. I did add a small cheap powerhead to the tank just so I wouldn't have stagnant water in my entry way room. I did use rock work from my old tank that I had let dry out, which Im sure had die off. Could that have been enough to start a cycle? If the water has already gone through a cycle, does a fresh water cycle differ from a salt water cycle? Could I just do a water change and start adding salt?
I did throw a piece of raw shrimp in there just now to see what happens. How long would it take to see any ammonia readings (if the tank didn't actually cycle)?
Curious to hear thoughts!!

 

[Mr. Bill]

Yes, your tank has most likely cycled. Unfortunately, freshwater bacteria cannot transition to saltwater and will die immediately once exposed. I made that mistake a few decades ago when I decided to convert a fw tank to sw. I added the salt, and the water instantly turned milky from the bacterial die-off. On the plus side, that was enough to launch a sw cycle, and the water cleared long before it was done.

 

[corey.nolta]

So I added salt to the water on Jun 25th, and brought the salinity to 1.026 and let that mix for a day. I then moved over a few good chunks of rock from my holding tank to help the cycling process along. I also added a piece of raw shrimp to the tank as well. It's been a week and I'm sitting at 0 ammonia, 0 nitrite, and 20 nitrate. Could there have been a cycle in just a week since I added established rock to the tank? That doesn't seem legit, but I tested twice and same results.