Let me start with a little background. I have a divided ten gallon with my two males in it, that currently is being treated for ich. My female is (or was) in a five gallon with four ghost shrimp.
So yesterday, I was doing a complete clean in the 5gal.. it really needed it. I basically changed about 90% of the water and vacced the gravel, but was a little hasty in refilling/reoccupying it and apparently shocked the shrimp. I didn't realize this until this morning, when I woke up and all four shrimp were dead. The betta (Willo) was perfectly fine. Moving, eating, not breathing heavily.
Just to be sure, I checked the water, and the nitrItes were at a insane 3... WAY above a healthy range. I wasn't sure if it was from the shrimp dying or not, so as soon as I got home I did about a 60% change to bring it down, intending to do more the next day. I had checked the water again before, and the nitrites were down to about 1.5.. which was strange, since I hadn't done anything to it. After that, I changed the ten gallon (for the ich treatment) and acclimated everyone back in.
Offhandedly I checked the water a third time afterwards, and the nitrites had gone back UP to 2! Frustrated, and sudenly doubting my test kit (and my carefully treated water), I checked the ten gallon's water and the nitrites came back at... 0.
So it's not my house water, it's not the test kit. What could I be missing?
The tanks are on either side of my desk.. the five gallon is closest to the window, but not in direct sunlight. They're both at ~82*, and both filtered.
In addition to that, it just occurred to me that I should probably get Willo out and into a temp tank. She's active and breathing fine, but I'm thinking to maybe just do it anyways.
edit; actually, yeah, going to move Willo out for the night or until I can get this cleared up. Anyone have any thoughts on why it would spike, though?