Ever wonder about the effects of coral toxins or rusty aquarium gear on your aquarium inhabitants? What about something as simple as sticking your hands in the tank? These pollution challenges are multifaceted and the results are almost always accumulative where the effects show up over time. In the ocean, these toxins are quickly diluted due to the vast water volume. In our aquariums, they'll build up if we don't have a plan in place to deal with them.


Biological Warfare (allelopathy)

Allelopathy: The use of chemical compounds to suppress the growth of competitors.

Biological warfare, or allelopathy, is a fascinating and complex phenomenon observed in saltwater aquariums, mirroring the competitive interactions found in natural coral reefs. Various organisms, including corals, algae, and microorganisms, engage in chemical warfare to secure territory and resources. They release toxic biochemicals into their environment to inhibit the growth or survival of competing species. However, unlike in the ocean where these toxins rapidly dilute, these chemicals can accumulate, leading to stress and potentially lethal outcomes for the tank inhabitants.

Biological Toxin Sources can include:

  • Cyanobacteria
  • Algae - Direct Contact or Algae Extracts
  • Dinoflagellates
  • Corals Themselves - Typically linked to soft corals

The Solution: Investing just a few dollars in activated carbon can remove many toxins. Additionally, using a protein skimmer can further reduce their presence, and for even more effective breakdown of these toxins, employing an ozone generator can be highly beneficial.

Carbon in Media Bag
Ozotech Ozone Generator



Pollution from additives represents a multifaceted challenge that demands careful management. Additives, essential for maintaining the health of the aquarium ecosystem, can inadvertently introduce impurities if not formulated or used correctly. These impurities, accumulated over time, can stress or even kill the inhabitants by bioaccumulating in the coral's tissues. Moreover, the formulation of these additives is a delicate balance. A mismatch between the uptake of various elements by the corals and the replenishment provided by additives can lead to an excess of certain elements, turning beneficial substances into pollutants.

Ultimately, every additive will have impurities. A while back, we ICP-MS tested calcium and alkalinity additives for impurities. In this test were aquarium specific additives as well as popular DIY options. What we found were grossly different levels of heavy metals, copper, and other impurities. None of them were perfect. Any impurity sounds bad, but remember these impurities are diluted in our aquariums and only become an issue over time if other best practices discussed here aren't being followed-- regular water changes being a leading solution. 

Additive Purity Test
Additive Purity Test Settling Cones

Another significant concern is the rise in salinity due to the sodium chloride left behind from dosing two-part additives, which, if not managed, can stress aquatic life. ALL two-part dosing products raise salinity because they're all based on salt. The calcium part is based on calcium chloride, while the alkalinity part is based on sodium carbonate. When added to the tank, the alkalinity ionizes into the water leaving the sodium behind. The calcium ionizes into the water leaving the chloride behind. Sodium + chloride = Sodium Chloride...Salt! While maybe not an issue a day, week, or even a month later, this increase in salinity can cause cumulative issues if not checked and managed over time.


Salt Mix

Pollution can also stem from the very foundation of the aquatic environment: the salt mix. While most salt mixes are designed to mimic natural seawater and support marine life, variations in quality and formulation can introduce potential pollutants. The quality of a salt mix determines the baseline chemical composition of the aquarium water. Impurities or imbalances in a salt mix can lead to elevated levels of certain elements or toxins, which, over time, can accumulate and adversely affect the health of the tank's inhabitants. Furthermore, inconsistencies in the manufacturing process or the sourcing of raw materials can result in batch-to-batch variability, posing a challenge to maintaining stable water parameters.

The Solution: There are certainly some that are better than others, but most are what we'd classify as "good enough" from a contaminant perspective. For most of reefers, picking a brand of salt mix you believe in and sticking with it is wise. Historically, we've used Tropic Marin Pro Reef and HW Marinemix Reefer salt mixes with good results.

Hands & Air

Seemingly innocuous sources like our hands and the surrounding air can also contribute to pollution in our aquariums. The myriad substances we come into contact with daily, such as lotions, soaps, and various household chemicals, can inadvertently contaminate our tanks when we immerse our hands or arms without thorough cleaning. Moreover, the air around the aquarium isn't a benign carrier; it can harbor aerosolized pollutants, volatile organic compounds, and even elevated levels of carbon dioxide from respiration, all of which can dissolve into the water column through surface agitation or protein skimmers. These airborne contaminants can create an acidic environment, inhibiting coral calcification and leading to stress or disease in marine life.

The Solution: Emphasizing the importance of preventive measures like using gloves, minimizing hand to tank contact, and employing carbon filtration or air purification strategies. Coupled with regular water changes, these tactics can significantly mitigate the risks posed by these indirect pollution pathways.

Arm Length Gloves
Air Pollution


Old, Rusty Equipment

Deterioration of equipment is an often-overlooked source of contamination. Over time, aquarium gear such as heaters, pumps, and magnet cleaners can suffer wear and tear from constant exposure to saltwater, leading to rust, corrosion, or the release of harmful substances when seals fail or plastics degrade. Such events can introduce significant pollutants into the tank, leading to rapid declines in water quality and posing immediate threats to the health of its inhabitants. 

The Solution: Proactive maintenance, including regular inspection and cleaning of equipment with citric acid or similar solutions, is crucial in preventing these catastrophic failures. By ensuring that all gear is in good working condition and replacing any items showing signs of wear or damage, aquarists can significantly reduce the risk of equipment-related pollution. Additionally, having emergency response tools like specialized resin media on hand can provide a crucial lifeline, allowing for the rapid removal of contaminants should a failure occur.


Final Thoughts

This sounds heavy, but the solution is light and involves practices that many of us are already doing.

  • Clean your pumps and other equipment every 6 months.
  • Perform routine water changes
    • 35% Monthly
    • 10% Weekly
    • 1.5% Daily
  • Use Carbon or Ozone.
  • Use resin like Purit in an emergency.

These proactive solutions will solve a vast majority of pollution challenges. The real value of this information is understanding why the good practices you're already doing are why you're successful. Don't stop doing them or you'll let pollution silently build up.