No scientific study, but just my experience...
I cycled my 10g QT with a cocktail shrimp, but didn't realize I didn't need a whole one for just 10g. At 3 weeks after getting a trace of ammonia, my ammonia levels were at 6.0+ppm
, and I still hadn't seen any nitrites. At that point, I did a 50% PWC
and got my ammonia down to 3.0+ppm
. Two days after that I did another 50% change and got it down to around 1.5. I still hadn't seen any nitrites, and I was 3 weeks and 4 days into the cycle. Two days after I did that 2nd PWC
, I finally detected nitrites and my ammonia started to drop. Two weeks after that point, my cycle was finally done. The cycle took just shy of 7 weeks.
Perhaps it was just coincidental that my nitrites finally showed up only after I substantially lowered my ammonia. Except...
Fast forward 3 months or so after I've broken down the QT and disinfected it. I'm ready to cycle it again. This time I control the ammonia source better and only let it get to 0.75ppm ammonia. Within 10 days I had nitrites showing up. After 5 weeks the tank was completely cycled. (And is home to a very perky Bangaii Cardinal, in his 3rd week of quarantine.)
Granted, the difference between 5 and 7 weeks for a cycle isn't a big deal. But I did find it interesting that with the super high ammonia levels, my tank took 3 weeks to show any signs of nitrites - but with lower ammonia levels it took only 10 days to show signs of nitrites.