Possible but highly unlikely
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but hey stranger things have happened
OK lets start from the beginning.
What is in your tank that is new and what came from an established tank.
I know you have some ornaments from another tank but I wouldn't have thought that alone would be enough to cycle a tank that size that quickly.
When did you take your first tests and did you test every day of that first week? IF you didn't it's possible you missed your ammonia cycle and are now waiting the the nitrite bacteria to grow. I've never cycled with those pellets so have NO idea how rapidly they would produce ammonia.
Your original results had a little nitrite as well which could quite possibly be in your water as well. If it continues to rise and ammonia stays at zero then I will have to say YES your ammonia munching bacteria is in place. It would be really odd to have that bacteria present this soon but heck the time for cycling a tank is anywhere from 2-6 (or more) weeks just remember the bacteria on the ornaments will be producing small amounts of Nitrite and nitrate. You could very well be 1/2 way there already.
You will see a steady increase in the level of Nitrate when your cycle is set and the others will be 0 or very close to it.
I have a little 14.5 inch cube that has been running for almost a week now with just under 10 gallons of water in it. New sand, plants, rocks and filter. 3 days ago I took the filter out and ran it in the base of my husbands big canister filter for an hour while he was cleaning it. This water was chock FULL of dislodged bacteria so I seeded the filter with it. Then I put 1L if the bacteria filled water straight into the tank and put the filter back in again and it still wasn't enough to avoid the cycle process completely I had an ammonia spike yesterday (0.5) so It's still cycling.
I have all the bacteria present, every thing being produced, but they are not present in high enough numbers yet to neutralize all the ammonia being produced by the one 10cm axolotl that has been in there for 2 days now.
If you're anything like me you are anxious to get your new pet. You can cycle with an axie in there using them as your ammonia source. If your comfortable that you can keep on top of your water quality there is no reason you can't put an axolotl in there now. I wouldn't worry about the guppies if you get one big enough to eat them. They don't tend to be fin/gill nippers so should be find for the time it takes for him or her to eat them.
I'd LOVE to see dome pictures of this monster sized tank when you get a chance :happy: