Nitrites, metals and biomedia: debunking the misinformation.
In recent years, thanks to the massive spread of social media and the growing desire to simplify marine aquarium management, some old urban legends have returned to circulate, appropriately reformulated for today's audience. One of the most dangerous is the one that attributes to biomedia - often generically labeled as "porous materials" - the responsibility for the accumulation of nitrites, the release of heavy metals into the tank and in general their uselessness or even danger.
Stop everyone.
These are intolerable scientific blasphemies, absolutely harmful to enthusiasts who might believe them.
We will address point by point, with the support of scientific bases, technical literature and decades of practical application in various sectors, the incorrect statements that are spreading, clarifying the functioning of biological substrates, the nitrogen cycle and the real origin of the alleged "problems" connected to the use of these materials.
Where do nitrites really come from?
Let's start with an inconvenient truth: if you find nitrites in your aquarium, it's not the bacterial support materials that are to blame, but rather the fact that the nitrogen cycle is not working properly.
Point.
Nitrites (NO2-) do not appear by magic, nor are they “released” out of thin air: they are the intermediate product of the metabolism of nitrosating bacteria, which convert ammonia (NH3/NH4+) into nitrite. Under optimal conditions, this nitrite is immediately converted into nitrate (NO3-) by the second-stage nitrifying bacteria.
When we find nitrites in the tank, it means that:
· the organic load is too high compared to the oxidation capacity of the system
· the surface area available for bacterial colonization is insufficient
· the filter maturation is incomplete or has been disturbed by the use of chemicals
· the bacterial biofilm has been removed or damaged
· the water flow in the system and the exchange with the sump are poorly designed (too slow or too fast)
· the chemical-physical conditions in the sump (pH, salinity, temperature, oxygen) are unfavorable to the growth of nitrifiers
Attributing all this to “porous materials” is wrong and dangerous: it distracts attention from the real causes and pushes the aquarist to remove the very tool that could help him solve the problem.
What Really Happens in Bacterial Substrates
A biomedia does not work miracles immediately, but those who tell you that it does harm are simply manipulating enthusiasts, making dangerous disinformation. High specific surface materials have been used for decades in aquaculture, water treatment, public aquariums and industrial plants.
Their function is simple: to provide accessible and protected surfaces for microbial colonization.
When biomedia is placed in an area of the sump with moderate flow and good oxygenation, the pores become colonized by aerobic bacteria, particularly:
nitrosating bacteria (oxidizing NH3/NH4+ to NO2-)
nitrifying bacteria (which oxidize NO2- to NO3-)
If the system is balanced, no nitrite will be measured.
If, however, nitrites rise, it means that phase 2 of the cycle is limited, and in that case the reasons can be multiple and extremely varied.
Removing the biomedia at this stage, because according to these self-styled experts “they release nitrites”, is a serious mistake. On the contrary, the solution is rather:
· enhance filtering and correct deficiencies
· insert an algal component into the filtering if it is absent, enhance it if it is present
· improve oxygenation of the system
· maintain a calibrated and constant flow of water and oxygenation in the biomedia
· avoid aggressive or too frequent cleaning of the filter media
· try to promote the establishment of bacterial biofilms
· avoid the use of easy and immediate solutions based on chemicals
The nitrogen cycle is not a magic formula (or even an immediate one)
One of the most common mistakes in aquarium keeping is to think of the nitrogen cycle as an immediate, instantaneous and always linear formula.
In reality, each phase of the cycle requires time, specific conditions and, above all, mature microbial populations adapted to the environment.
No biological filter starts working as soon as it is turned on.
Nitrifying bacteria have relatively long replication times compared to other microorganisms (in some cases even 12–24 hours), and require a stable substrate, access to nutrients and precise chemical-physical conditions.
If these conditions are altered — even temporarily — a temporary imbalance may occur, during which neighing may appear.
It is a response of the system to a disturbance, not a defect in the technique used for their natural biological reduction or in the filter material.
It is important to distinguish between:
· colonizable substrate (biomedia): provides a home for bacteria
· environmental conditions (flow, oxygen, temperature, pH, salinity): determines which bacteria thrive there
· active microbial population and specific strains: the real driving force of the process
It is not enough to “put something in the sump” to complete nitrification. It takes time, it takes stability, it takes management consistency.
Furthermore, nitrifying bacteria are not all the same: recent studies have shown that Nitrospira inopinata, for example, can complete both phases of the cycle (comammox), but only under particular conditions and which require techniques not yet adopted by our sector.
Other bacteria, however, compete for ammonia or nitrite, and the success of one or the other depends on minimal, often overlooked, environmental parameters.
Over time, a mature aquarium tends to develop a stable microbial ecological succession, in which each niche (from the glass surface to the innermost porosity of the substrates) hosts a specific type of bacterial community or consortium.
It is precisely this diversity, favored by the presence of biomedia, porous rocks and other colonization substrates, that guarantees the biological stability of the system.
In extremely simple words:
· There are no materials that magically “make nitrites disappear”.
· There are no materials that “create nitrites” on their own
· Nitrites appear when the system cannot metabolize them quickly enough
· Removing biomedia in response to this is like cutting the brake wire on a car, because it brakes poorly.
Promoting the idea that porous materials “generate” nitrite or prevent its removal is a deliberate disregard of decades of scientific literature on biofilms, nitrification and biological management in aquaculture, in an attempt to influence the market with incorrect, unscientific and unfounded claims.
Here is a small summary table to help you better understand these concepts and avoid making misleading statements.
|
Transformation (reaction) |
Most common marine microbial species/consortia |
Typical Tank Habitat & Metabolic Requirements |
|
|
0 |
Proteins → NH₄⁺ (mineralization) |
Vibrio , Pseudoalteromonas , Bacillus spp. |
Biofilm on rocks and biopellets; pH 7.8-8.4; medium-high O₂ |
|
1 |
NH₃/NH₄⁺ → NO₂⁻ (ammonium oxidation) |
Ammonia-oxidizing Archaea (AOA) : Nitrosopumilus maritimus • Ammonia-oxidizing Bacteria (AOB) : Nitrosomonas marina , Nitrosococcus oceani |
Well oxygenated bacterial film on technique, biomedia, rocks, sand; salinity 34-36 ‰; temp. 24-27 °C |
|
2 |
NO₂⁻ → NO₃⁻ (nitrite oxidation) |
Nitrospira marina , Nitrospina gracilis , Nitrococcus mobilis |
Same substrates / biomedia as phase 1; O₂ > 4 mg L⁻¹; Ca²⁺ & HCO₃⁻ sufficient as “buffer” |
|
3rd |
NO₃⁻ → NO₂⁻ → NO → N₂O → N₂ (classical denitrification) |
Paracoccus denitrificans , Pseudomonas stutzeri , Shewanella denitrificans |
O₂ zones < 0.5 mg L⁻¹: fine sand depth >3 cm, pores of living rock, biomedia, sulphur reactors; C-org from vodka/acetate/biopellets |
|
3b |
NO₃⁻ → NH₄⁺ (DNRA) |
Vibrio splendidus , Sulfurimonas spp. |
Very fine sand with high organic matter (anoxic, redox < 0 mV) |
|
4 |
NH₄⁺ + NO₂⁻ → N₂ (ANaerobic AMMonium OXidation) |
Planctomycetes “anammox”: Candidatus Scalinua profunda |
Anoxic pockets in old DSB/under-washed zeolite filters; requires NO₂⁻ present |
|
5 |
NO₃⁻ → assimilation in algal biomass |
Macroalgae ( Chaetomorpha , Caulerpa ), cyanobacteria |
Illuminated refuge; PO₄:NO₃ ≈ 1:16 (Redfield) |
How to read the table
· Phases 1 + 2 are aerobic, so they occur where the water is well-moved (surface rocks, filter sponges, plastic rotors).
· Stages 3-4 require little or no oxygen; this is why fine sand beds, sulfur reactors or slow biopellets are needed.
· In a reef aquarium, much of the ammonia is oxidized by AOA archaea (Nitrosopumilus), which are much more abundant than AOB at full salinity.
· The DNRA (3b) and anammox (4) pathways are minor but explain why unexpected ammonium sometimes appears in mature tanks with no measurable nitrite.
The myth of metals in biomedia
One of the most common myths is that so-called “porous” filter materials — especially those used as biological media — release heavy metals (aluminum, zinc, copper, barium) detectable by ICP-OES.
This unfounded claim deserves to be methodically dismantled.
First of all, we must distinguish between:
· biomedia designed for aquariums (often based on glass porcelain, sintered, special ceramics or polymeric materials)
· industrial ceramics not intended for aquatic use
In the first case, the materials are specifically engineered to be stable and inert in seawater. The fact that they contain silica, alumina or any other oxides does not imply release at all, since these compounds are structurally bound in glassy or crystalline matrices that are totally insoluble in our systems.
In the second case, using undeclared materials, of unknown origin or deriving from other sectors (construction, thermal construction, DIY), can actually represent a risk.
But this is not about quality biomedia, it's about improvisation.
In fact, among the sources of metal contamination, the most important and common are:
· Foods fortified with non-chelated trace metals
· Low quality solid sea salt, with metallic impurities or defects in the mixing
· “Magic” supplements/medications/products that contain copper or zinc
· Synthetic and natural rocks (dry), untreated
· Phytoplankton grown with inadequate fertilizers
· Unsuitable osmosis systems or exhausted deionizing resins
· Metal pipes or fittings downstream of the osmosis
· Technical plastic pipes (e.g. riser) made of unsuitable material
· Colored plastic tubes (e.g. from dosimeters) made of unsuitable material
· Resistors, thermostats, pumps and other technical instruments with damaged sheath
· Magnets with damaged coating
· Rusty metal clamps, hinges and clamps in sump
· Tools (pliers, scissors, tweezers) not stainless steel, rusty
· “Antiphosphate” granules based on exhausted and friable aluminum oxide
All these sources of contamination (and unfortunately the list is not exhaustive…) are sufficient by themselves to cause an increase (whether rapid or progressive) of the values. Wanting to attribute everything to “bricks and balls” without excluding the primary causes is misleading, tendentious and totally irresponsible.
Let's debunk the false myths point by point
In this chapter we report, one by one, the main misleading statements spread online, with the relative technical and scientific denials. Forgive the clear and direct tone, but we cannot stand this populist and pseudoscientific rhetoric that does nothing but compromise the correct management of reef aquariums and confuses enthusiasts, creating damage to the entire sector.
❌ "Porous materials release nitrites"
False. Nitrites are the result of a biological process. No inert material "releases" them.
If nitrites increase, it is because the population of nitrifying bacteria is not sufficient to complete the cycle.
The cause is in the management, not in the material.
❌ "The “bricks” and “balls” contain heavy metals that are released into sea water"
Misleading and fundamentally incorrect. Even if they do contain metal oxides, their structure is, in the vast majority of cases, glassy/crystalline and insoluble.
If metals are detected in ICPs, moving metal components, oxidations, contamination by salt, feed, additives, osmosis must first be excluded.
Biomedia is the last thing to blame, not the first. This is not meant to be a tendentious generalization, each biomedia is different, there are infinite products on the market, even extremely different ones.
Wanting to give a single judgment valid for everyone would be approaching science and the work of the manufacturing parent companies with arrogance and presumption.
❌ "Since everyone has been using biomedia, problems with nitrites have increased"
Big logical shortcut, totally non-functional. Correlation does not mean causality. A lot has changed in the last 30 years, the fact that two random and indistinct events occur at the same time, does not imply that one causes the other. Furthermore, we believe it is necessary to reiterate, biomedia are widely used in aquaculture and industrial purification, for several decades, and with excellent results.
I find this a fundamentally arrogant, simplistic and disrespectful statement towards the work of all those researchers who continue to bring innovations in the field of materials engineering.
❌ "Biomedia slow down the nitrogen cycle in marine water because they were born for fresh water"
False. The nitrification processes are identical in fresh and marine water, only the predominant bacterial species change.
The inert supports can accommodate both indifferently.
What matters is the ripening time and the environmental conditions.
❌ "Companies do not declare the composition of the materials"
Generalization. Serious companies publish technical specifications, detailed data sheets and — where necessary — even chemical analyses.
If you don't trust a manufacturer or a product, just don't buy it.
But insinuating generalized doubt is a clear form of misinformation.
❌ "Just remove the materials to make the nitrites disappear"
Deceptive. This is a typical post hoc correlation.
Removing biomedia may have the side effect of temporarily reducing oxidation (and thus apparent nitrite levels, at the expense of increasing ammonium), but it is not a solution.
It's like turning off a thermometer so you don't see a fever.