I’ve spent a lot of time involved in the saltwater fish and coral hobby. I’ve owned an aquarium maintenance and design company, I’ve been a volunteer SCUBA diver at a public aquarium, and I’ve personally kept saltwater aquariums for the past 15 years. In that time I’ve fielded a lot of questions from friends and family about all-things saltwater fish, and one of the main questions I’ve been asked is “How do I achieve perfect water quality”. The answer is, you don’t…
Perfect water quality is a myth. It doesn’t exist. Not in the world’s oceans, and certainly not in the small glass and acrylic boxes we keep in our homes. No matter how often you perform partial water changes, and no matter how good your filtration is, you will never achieve perfect water quality. There will always be dissolved organic compounds and nitrates in your water, but that’s OK. Your fish and corals do not require perfection, but they do require clean, stable water. So rather than focusing on something you can never attain, let’s focus on what you can accomplish.
Clean, healthy aquarium water starts with a properly set-up tank. The tank should be as large as you can afford and accommodate. Ideally the aquarium should be “long” rather than “tall”, and it should have a lot of water movement. The surface of the water should be moving vigorously, which promotes gas exchange and facilitates nutrient and waste export (often called filtration). While it is possible to keep saltwater fish and corals without the use of a protein skimmer, I would not recommend it. A protein skimmer is the single best filtration system available, and should be included in any saltwater system set-up. Lastly, the use of porous rock (preferable live rock) and sand is heavily recommended, as these provide a great deal of surface area for beneficial bacteria to grow upon and thrive.
Once you have your aquarium properly set-up and stocked, you’ll need to maintain it. The single most important thing you can do for your fish and corals is the partial water change. Partial water changes are exactly what they sound like. You’re removing a certain amount of water from the tank and replacing it with freshly mixed saltwater. In doing so, you dilute the toxins and pollution in your aquarium, and you import fresh trace elements (iodine, calcium, magnesium, etc) that the fish and invertebrates require for proper growth and health. There’s no on-size-fits-all approach to water changes, but I would recommend at least a 10% water change every 2-3 weeks. 15-20% is better, especially if your tank is smaller or more densely stocked with fish. The larger the aquarium and the less densely it is stocked, the longer you can go between water changes. But even with the largest aquariums (200+ gallons) I would never recommend that you go more than 3-4 weeks between water changes.
The other aspect of water quality that you’ll want to focus on is what you are putting into your aquarium. By that I mean the foods you are feeding your fish, corals, and invertebrates. In a closed system, fish and invertebrates live in the same water that they export their waste into, so in addition to frequent partial water changes you’ll want to minimize the amount of uneaten food that breaks down in the water column. A varied diet is important, so I would recommend a good quality pellet food for omnivorous fish every day (I use and recommend New Life Spectrum Marine Formula) as well as daily nori sheets. I typically feed my fish-only tank with some frozen food in the afternoons (large chunks of shrimp and clams on the half shell for the puffers, and frozen Formula 2 and Angel formula for the tangs and angels). In my reef tank, which houses live corals and invertebrates, I eliminate the frozen food, as it breaks down and degrades water quality much more often. I would also recommend that you not heavily supplement your reef tank with coral foods. These tend to pollute the tank very quickly. If you’re keeping up with your frequent partial water changes and your lighting is high-intensity, your photosynthetic corals should receive the majority of their food automatically. I use a supplement (Coral Accel) once every two weeks, right after I have completed the partial water change.
Keeping saltwater fish and corals is a lot easier these days than it used to be. If you set-up your aquarium properly and adhere to a consistent and frequent maintenance program, you too will be able to create and maintain a thriving saltwater ecosystem in your home.