Corals Dying

[Moogled]

Sorry, I went out to buy new test kits just in case these older ones wouldn't work.

I did a 30% water change two weeks ago with another 10% the day after. My nitrites were coming up as 0.25.

My current parameters are:

Ammonia: 0.25
Nitrate: 0
Nitrite: Undetectable

I do regular water changes and feed moderately and try to keep Ammonia as low as possible. I've had this tank for almost a year now, shouldn't ammonia be undetectable unless it was a spike? All my fish are fine and swim around happily. There's no odd behaviour (e.g gills showing) of any sort.