Unexplained ammonia spikes

[finch]

Another thought: are your plants healthy? If they're melting or dying back, that could release ammonia. Especially if you've got a lot of stem plants or floaters.

[Flynnex]

Y'all are overcomplicating it. Bet it's just a dead snail. OP, poke around the tank with a net, see if you find anything funky.