Sometimes hobbyists put livestock into their aquarium before the “cycle” has run its course (referring to the nitrogen cycle of course). The ammonia or nitrite in the tank spikes, or reaches their highest concentrations, and the fish or corals are being subjected to this deadly water. For more than obvious reasons, the livestock does very poorly and oftentimes dies. If this is encountered, the only real remedy is to get the livestock out as soon as possible. If there are no fellow hobbyists that can house your livestock, the next best thing is to perform as many water changes as possible, the larger the volume changed the better, until the ammonia or nitrite levels come down to zero.