When I got home today found my firefish dead he was eating fine and swimming before today. Just cycled my tank its a 90 gallon. Salinity is at 1.022 (hydrometer might be off?) Ammonia 0 nitrite 0 nitrate 30-40ppm what could of caused him to die
Nitrates are a little high (aim for 0 but up to 10 is ok) I would perform a big water change to bring those nitrates down. Also how long had you had it? How did you acclimate it? Who are his tank mates?
Just a porcelain crab and emerald crab drip acclimated him and had him for a week I did a series of water changes and they didn't really budge so I was going to do 10% weekly but he only lived a week so...
It can be at times. Think about it like this. Doing a 10% water change, when your nitrates are 40 you are only removing 4 leaving you with 36. This is why we are recommending much larger and more frequent changes to bring the number down. That is, if that is the issue of course. There were no signs of distress?