Check nutrients in the aquarium - our tip:

Nutrient levels that are too high or too low are signs that something in your system is not working properly. Are you changing the water regularly? Is the fish density perhaps too high? Are you feeding too much or too little? Are there enough nutrient consumers in your system, such as macroalgae and corals? Is the filter performance sufficient? All of these can be helpful questions to get to the source of the problem.