We Want Answers to Phosphate & Nitrate in Reef Tanks. Can Our Approach to Nutrients End the Debate? | 52SE
Have you ever wondered where the line between necessary nutrients and detrimental pollution lies in your reef tank? It's time to unravel the complexities of food, nitrates, and phosphates in reefing. We tackle the big questions: What are the optimal nutrient levels for your tank? How do these substances transform from beneficial to harmful? And how can we balance the delicate ecosystem within our aquariums? Get ready to challenge your assumptions and deepen your understanding of what it takes to sustain a healthy, vibrant reef environment.
The Biggest Source of Pollution
The daily addition of fish and coral food is by far the biggest source of pollution in modern reef aquaria. Foods as a source of pollution is a challenge that's addressed in every successful aquarium. Foods are nutritive by nature and required for survival and even the broken-down organics and residual nitrate and phosphate can be beneficial. That's until the import and export find themselves out of balance and start rising. At some point, they become pollutive.
Most aquarists would agree to the simple statement of "no fish or coral wants to live in polluted water," but we might not agree on what polluted water means. Let's start with the actual definition of pollution. Pollution: A substance that has harmful or poisonous effects when sufficient quantities are absorbed, respirated, or ingested. Some pollutants may cause immediate mortalities, while others may make the fish or coral sick or more susceptible to illness or disease.
Nutrients (Nitrate & Phosphate): Near to mid-term problems that are easily correctable at almost any point.
Everything Else (unused Vitamins & Minerals): Longer term problems with many in this category not easily tested for, even with ICP testing.
It's a topic that almost nobody thinks about...the toxic accumulation of excess minerals from foods. While most reefers probably agree that food can be a pollutive substance, we don't usually think of pollution as a poison. What about the vitamins and minerals in our fish food? There is zero chance that they're added in the exact ratio our fish and coral uptake them in. This imbalance? Left to build up in our tanks.
While some elements are surely more harmful at elevated levels than others, there's an easy way to avoid these issues all together. You've probably implemented many of these on your reef tank already. Examples include protein skimmers, roller filters, algae scrubbers, macro algae refugiums, and water changes.
Nitrate and Phosphate
The right answer is NOT universal; it has to be applied to a goal. Our goal: a safe range for these 7 tanks, multi-year success, and an approach that doesn't require us to play mad scientist with different chemicals, filtration media, and constant water testing.
Goal: 0.1 ppm
Operating Range: 0.05 - 0.15 ppm
This goal and range are achievable by a wide range of skill sets, common equipment, and maintenance practices. We'll measure phosphate once per month and track it. As long as it's not perpetually rising month after month, we'll know our approach to phosphate control is working.
The ratio of nitrate to phosphate in most fish foods is commonly in the range of 5:1 to 30:1. With our 0.05 - 0.15 ppm phosphate goal, we expect our nitrates to land somewhere between 0.25 - 4.50 ppm. We'll track nitrate along with phosphate and adjust our maintenance plan if necessary.
Inorganic vs organic sources of nitrogen and phosphorus: Something only a small portion of the hobby has embraced.
Inorganic Nitrate and Phosphate: Nearly completely broken down and testable with commonly used test kits. It's also readily available for uptake by algae and other pests.
Organic Nitrate and Phosphate: Fish Food/Waste, Bacteria, Plankton, Coral Food. Less available for algae, but still available for corals to consume, depending on the particulate sizes.
Historically, the goal for many was to achieve nearly undetectable levels of nutrients, aligning with the belief that "cleaner" water would result in healthier and more vibrant coral reefs. This led to widespread use of nutrient-removing technologies like GFO (Granular Ferric Oxide) and aggressive water change schedules. The mantra was almost universally "the lower, the better" for phosphates and nitrates, with many striving for near-zero levels.
However, over time, as the understanding of coral biology and tank ecology deepened, it became clear that this extreme approach sometimes did more harm than good. Scientists and experienced hobbyists began to notice that while algae growth was inhibited, coral health could also be compromised. The very low nutrient levels affected the symbiotic zooxanthellae within the corals, which are essential for their health and coloration. These algae provide corals with much of the energy they need through photosynthesis, and starving the system of nutrients also starved these symbionts.
Now that we have a goal, how does someone actually achieve and maintain 0.1 ppm phosphate and the related level of nitrate in a reef tank without the constant use of phosphate removers? The answer is simple: if the levels drift out of your target zone, match the food input to the export (filtration).
Water Changes: We recommend a 1.5% daily, 10% Weekly, or 35% Monthly water change.
Food Input: Feed less, when it makes sense. Don't starve the animals, but if 20% less food would go unnoticed, try that. Also consider changing what you feed. Frozen food is less nutrient dense than pellet foods due to the water content, so it's a lot harder to overfeed. Consider making your own frozen food to tailor the ingridents to your tank's specific needs.
Protein Skimmer: A protein skimmer can remove much of the excess food and nutrients before they break down, but if it's working too well, consider putting your skimmer on a timer and not running it 24/7.
Roller Filters: Catches uneaten fish food and waste before it breaks down. Most useful early on when the corals are small and there isn't as much uptake vs reef tanks with massive colonies.
Algae Scrubbers or Refugiums: The algae can bioaccumulate toxins and heavy metals, making it extremely easy to remove them from the aquarium.