Reef Aquarium Algae Management: Nitrate & Phosphate Control

Paleontologists collected 21,000 sediment samples from the Neoproterozoic to present, analyzing carbon-to-phosphorus ratios. Terrestrial plants have a ratio of approximately 2,000:1, while marine algae have 100-106:1. The analysis revealed that 455 million years ago, the ratio suddenly jumped by a factor of 2, from 80 to nearly 210. This indicated massive terrestrial organic matter input. Within 5 million years, plants colonized Baltica, South China Platform, and Gondwana. By 445 million years ago, terrestrial carbon in marine sediments reached 40%, comparable to modern productivity.

The Redfield ratio (nitrate to phosphate ratio) is crucial for plant aquariums. During the first two weeks of startup, the ratio should not be maintained because nitrogenous compounds and phosphates will spike regardless of water quality. After the nitrogen cycle is established, the minimum optimal ratio is 0.5 mg/L phosphate and 10 mg/L nitrate. To monitor, add macro and micronutrients and test after three days - nutrients should be nearly consumed. For high-light aquariums preparing for photography, higher concentrations (1.5 mg/L phosphate, 25-30 mg/L nitrate) may be used. The ratio should be adjusted based on lighting intensity - higher lighting requires higher Redfield ratios.

Alfred Redfield discovered the ocean maintains a consistent nitrogen-to-phosphorus ratio of approximately 16:1 (or 10:1 when converted to nitrate/phosphate). Different organisms have preferred ratios, and meeting those needs allows them to thrive while competitors struggle. At extreme ratio ends, some organisms excel while others fail. The debate centers on whether concentration or ratio matters more for reef health—most evidence supports emulating natural seawater concentrations as the highest percentage approach.

The Redfield ratio (16:1 nitrogen to phosphorus) was derived from surface algae and deep water samples, not from coral reef environments. Coral reefs have ultra-low nutrient conditions that are very different from the ocean surface water where Redfield conducted his research. Applying the Redfield ratio to reef tanks is incorrect because reef corals evolved in environments with extremely low nutrients, not the nutrient levels that would produce a 16:1 ratio. The ratio is not valid for reef tanks or wild reef environments.

The Redfield Ratio (106:16:1 for C:N:P) is a statistical observation of average marine phytoplankton composition from the 1930s, not a biological requirement for individual organisms; reef aquariums should prioritize stable, clean water conditions over rigid adherence to this ratio, as different marine organisms (corals, algae, clams) have vastly different elemental requirements that vary by species, habitat, and symbiotic relationships.

An Algae Turf Scrubber (ATS) is an alternative to a traditional refugium. It consists of an enclosed acrylic box with a mesh sheet inside that algae grows on. The system is lit with LED technology and the algae is scraped off weekly and discarded. ATS units can be placed above the sump and allow water to trickle down, removing nutrients. They are particularly useful when space is limited, as they can fit in smaller areas compared to a full refugium compartment.

When water changes no longer work, refugiums and scrubbers are progressive solutions. Refugiums work by removing carbon dioxide, raising pH, and pulling out nitrogen and phosphorus. The speaker notes that full-spectrum lights (like Tropic Marin Tuna Sun) outperform specialized refugium lights. Protein skimmers are the next step, removing dissolved organics (essentially coral food) when nutrients are building up. Filter socks are used when corals want to eat all the food but organic waste is building up. Carbon dosing is the last option due to less experience and more moving parts. The speaker recommends starting with refugiums and progressing only as needed.

Algae serves as one of the most effective methods for nutrient export in aquariums, controlling nitrate, phosphate, and ammonia while stabilizing pH. Algae turf scrubbers, invented in the 1980s at the Smithsonian by Walter, differ from refugiums by cultivating filamentous pest algae in controlled environments optimized for growth. Modernized versions from Clearwater Systems offer compact, energy-efficient solutions that occupy less space than traditional refugiums. The technology requires LED lighting with specific wavelengths (660nm, 640nm red and 450nm, 420nm blue diodes) targeting photosynthetic peaks for vigorous algal growth. Water flows through slotted pipes, down the screen, and out through drains, with backup drains providing redundancy. Algae grows on the screen, removing excess nutrients, which are then harvested periodically to maintain system balance.

Two primary nutrient export mechanisms prevent algae growth by removing excess nutrients. Macro algae cultivated in refugiums absorb phosphates and nitrates from the water column; regular harvesting exports these accumulated nutrients. Protein skimmers remove organic molecules before they break down into inorganic nutrients like phosphates that algae utilizes. Both systems work synergistically to reduce the nutrient concentration that fuels algae growth.

Algae turf scrubbers actively remove excess nutrients from reef systems by growing fast-growing algae that consume nitrates and phosphates. Multiple scrubber units allow sequential cleaning cycles, ensuring continuous nutrient export. Regular maintenance involves scraping accumulated algae from scrubber surfaces to maintain effectiveness.

Nutrient levels directly affect coral coloration and health. When nitrates and phosphates are high, corals appear darker with vibrant pinks, especially at the ends. Low nutrients cause corals to appear faded and green. Different corals have different nutrient requirements - some like high nutrients while others prefer low. The golden jaw dropper is particularly sensitive to low phosphate levels. Phosphate can be dosed through the skimmer, overflow, or directly into the reef mat. Minimal dosing (around 1ml) prevents trace element issues.

The Ultra Low Nutrient System (ULNS) is a reef care approach that maintains nitrate and phosphate levels as close to zero as possible to achieve vibrant coral colors, requiring careful balance of all water parameters, regular water changes with foundation element supplements, trace element supplementation (A, B, C, D), and specialized feeding since corals in ULNS systems cannot rely on symbiotic algae for nourishment.

Coral color is the hardest thing to gain and easiest to lose in reefkeeping, with SPS corals being the most sensitive to nutrient levels and the first to lose color when parameters are off. Optimal nutrient ranges for SPS are nitrates 0.5-5.0 ppm and phosphates 0.02-0.08 ppm, while LPS and soft corals can tolerate higher levels (nitrates up to 10 ppm, phosphates up to 0.10 ppm). Both too low and too high nutrients negatively affect color—low nutrients cause pastel, washed-out colors while high nutrients reduce definition. To increase nutrients, feed fish more, add fish, cycle skimmers, reduce GFO, or decrease water changes. To decrease nutrients, reduce fish feeding, stop coral feeding, improve equipment, increase water changes, or implement carbon dosing. Trace elements and amino acids can manipulate colors but require advanced knowledge and careful dosing. Always make one change at a time and monitor results before making additional adjustments.

When nutrient levels drop near zero, corals starve and lose color. Plus NP provides balanced nitrogen and phosphate that symbiotic algae need to survive, supporting coral health. Amino Organic delivers vitamins and amino acids that form coral tissue and color pigments. Critical: Amino Organic should only be used after phosphate reaches 0.03 mg/L, as it doesn't add phosphate and can disrupt balance if used prematurely. The protocol is to first establish baseline nutrition, then enhance color and polyp activity.

In ultra-low nutrient reef systems, water changes serve primarily to replenish trace elements (like potassium, boron, and iodine) rather than remove nutrients, and blindly dosing trace elements without testing can lead to overdosing dangerous elements like zinc, copper, and nickel; even with low nutrients, adding nitrate back into the system may be necessary because elements like potassium deplete faster than expected, and high filtration systems like roller mats and macroalgae (such as Chaeto) can remove most waste before it breaks down into nitrates.