In the context of diagnosing diseases within aquariums, the initial and most critical tool remains the vigilant observation by the caretaker. As emphasized by cy.paul, being attuned to any deviations in fish behavior, appetite, or appearance is often the first indication of underlying issues. This observational method requires no additional costs or devices, merely a consistent and attentive approach to monitoring the health of the livestock.
While there are specialized diagnostic tools and apps available, the current feedback suggests a reliance on community knowledge and online resources. Darrie53 highlights the practicality of maintaining a simple log for tracking medication dosages and durations, which underscores the importance of maintaining organized records to identify patterns or improvements over time. Despite the technological advancements in monitoring systems, their cost and complexity appear to be barriers for some, leaving many to favor traditional, cost-effective methods.