the temp issue is resolved.
if you have nitrates, you might have had an ammonia spike and not caught it. Your LR
might have given you a small ammonia spike, but it may not have been strong enough to support the bioload of a fish.
ONLY DO THIS NEXT PART IF THERE'S NOTHING LIVE IN THE TANK-it's very early (7Am) and I haven't been to sleep yet tonight, so I can't remember if there's anything in the tank.
You'll want the ammonia to have gotten up to at least 4ppm, so I would test the tank by adding liquid janitorial ammonia. If you do it this way, you can only use the ammonia that doesn't foam when shaken, they only sell that type in hardware stores around here. Since your tank isn't that big, it'll likely only take a few drops of the ammonia to get it up to 4 ppm
. So add a few drops, let it mix for an hour and test ammo. If its not up to 4, add few more drops, repeat. Once it's up to 4ppm, leave it for 24h and retest ammo and test nitrites and nitrates. If ammo and nitrites are zero after 24 hours, then you're cycled. And you can add CUC and fish after a PWC