So yesterday I bought a 5 gallon tank from my lfs. It came with 2 used filters, (the original one was dodgy so he gave me a spare one for free) and a light. The media has been used but all the media was dry so there probably wasn't any good bacteria on them. He gave me some cheap gravel (which I later found out had loads of snails in!). So when I got home I washed the tank and the filters, but not the media. I put a layer of gravel from my other tank and put the other gravel on top. Then I filled half the water with the water from my other tank and half with tap water. My filter from my established tank is a sponge filter so I couldn't really put any media in the new filter. I then put some fish food in to start the cycle, and a few hours later I tested the water: the nitrites were just above 0.3, can't remember ammonia and the nitrates were at about 20 mg/l. Today, 24 hours later I tested the water and had 0 ammonia 0 nitrites and around 13 nitrates. Which is about the same as my established tank. Could the ammonia, nitrites and nitrates have spiked over night, if so could it then be cycled? And I am not planning on adding a betta for about 4 weeks anyway so I can wait for it to fully establish.

Thanks