Something looks wrong. Let’s figure out what changed.
Saltwater Aquarium Troubleshooting
When something goes sideways in a saltwater aquarium, the worst first move is usually buying a random bottle and changing five things at once. Start with what you can actually see, check the basics, and then use the guide that matches the problem.
Before you try to fix it
Four Things I Would Check First
You are not trying to diagnose the entire aquarium in five minutes. You are trying to separate an emergency from something you can identify carefully.
Look at the animals
Are fish breathing normally? Are corals damaged or simply closed? Is anything trapped, injured, or being attacked?
Check the equipment
Verify temperature, flow, water level, heaters, pumps, the ATO, and anything else that keeps the aquarium alive.
Test the basics
Confirm salinity and the water parameters that could change your next decision. Repeat a surprising result before chasing it.
Ask what changed
New livestock, heavier feeding, a missed maintenance job, a new light schedule, dead flow, source water, and equipment changes all matter.
Start with what you can identify
Choose the Guide That Matches the Problem
These are the two complete problem-solving guides that belong directly in this section right now. More can be added later, but only after the article is useful enough to earn its own destination.
Nuisance Algae
Use this when you need to identify common growth, understand what may be feeding it, and choose a response that addresses the cause instead of only cleaning the glass.
Dinoflagellates
Use this when the growth and behavior point specifically toward dinoflagellates. Identification matters because a generic algae response can send you in the wrong direction.
The problem may live somewhere else
Use the Existing Expert Guide
Not every problem belongs under one giant troubleshooting section. These subjects already have a better home, so this page should route you there without replacing that structure.
Water looks wrong or a test result changed
Start with accurate testing and parameter context before you correct anything.
A fish looks sick or acts differently
Use the fish-disease guide to stabilize the environment, observe the symptoms, and decide what the next safe step should be.
Power, heat, flow, or travel is the risk
Use the emergency-planning guide for outages, temperature events, vacations, and backup planning.
Keep the response simple
Change One Thing for a Reason
The goal is not to make the aquarium look perfect by tomorrow. The goal is to understand what is happening, correct the likely cause, and know whether the tank is actually improving.
A useful troubleshooting change
You can explain why you are making it, what result you expect, how long you will observe it, and what would make you stop.
A change that creates more confusion
You add several products, change lighting, alter feeding, clean everything, and replace media at the same time—then have no idea which change helped or hurt.
Still not sure where to begin?
Start With the Broad Nuisance Algae Guide
If the problem is unwanted growth and you do not know exactly what it is, start broad. Identify it first, then move to a more specific guide only when the evidence points you there.