What are nitrifyers?

Why would all your fish die in the last two days?

Possible reasons for all fish dying in the last two days could include sudden water parameter changes (such as pH or ammonia spikes), introduction of toxins or chemicals into the tank, diseases or infections spreading rapidly through the tank, or a malfunction in the filtration or aeration system leading to poor water quality. It's important to investigate and address these issues promptly to prevent further loss.