Colored or chromophoric dissolved organic matter or (CDOM) is a measurable component found in seawater. Phytoplankton, bacteria, solid substrate, decaying detritus, livestock and algal turf scrubbers are primary culprits behind this component and its recurrence in saltwater aquariums. Tannins released or leached out into the water bringing out a yellowish tinge to tank water. Also known as Gelbstoff or Gilvin, terrestrial freshwater run-off and in reef areas, seagrass beds and coral reef substrata are responsible for this dilemma in the natural environment. Dissolved organic matter has its merits as well as its downfalls. Because of this it is worthy to read and be aware of both scenarios to assist you and your unending journey to create and maintain a stable and healthy marine aquarium.
Because of the coloration of saltwater as a result of having dissolved inorganics in your water, your tank may not be as clear and beautiful as it could. Depending on the amount of dissolved organics in your water, water color can range from a greenish color to yellow to brown under extreme cases of excess organics in your water. Not only does this have an effect on your water quality and color but it can alter the amount of light and spectrum of light to your livestock below. If you will notice in natural reefs of the world the water is a crystal clear blue color. This is a result of lack of dissolved organics and other turbidity factors in the water. Take a look at the water on the coast of Connecticut…brown and cloudy due to excess plankton and dissolved organics. Coral reefs would never be able to survive here not only because of the varying temperature changes, but because of the lack of crystal clear water to allow the suns rays to penetrate into the water to support symbiotic coral growth. Nitrate limitations, lability and irradiance all factor in along with salinity elevation and temperature fluctuations either in a marine aquarium environment or out in the oceans of the world.
Turbidity, which is another term for suspended matter in water, can range from air bubbles, particulate matter, dissolved organic matter, plankton and phytoplankton. Similar to CDOM, though not as significant in small aquariums, turbidity will cause a change in the clarity of water. Making it cloudy almost as if a spawning has occurred within the water. This again effects the amount of light that is allowable to the livestock below and could be a direct result of whether a coral lives or dies.
CDOM and turbidity may also be a blessing in disguise for some living animals. Being that CDOM is yellow in color, it is infamous for absorbing the light at the blue/violet end of the spectrum. Photochemical and photobiological processes can be carried out by CDOM as well as its ability to block out the harmful UV rays of the sun or artificial lighting. Similar to the irridophores and bright pigments in corals like Acropora and Tridacna Clams, these components act as a sunscreen for the protection of its tissue against the suns intense UV rays.
There are ways of combating the accumulation of CDOM in aquarium water. Adding carbon, an ozonator or redox can assist in water purification by removing varying amounts of turbidity. These additives combined with your biological other chemical and mechanical filtration devices can provide pristine crystal clear water. The problem with using these devices is if you do not use these continually, what you are in essence allowing is, a dramatic change in the amount of the blue and UV rays, wavelength and Photosynthetic available radiation and usable radiation to corals and clams especially. Think of it like this: when your bedroom is dark as a result of your shades being closed and then you abruptly open the shades and the room brightens up immensely, this is what happens with the use of these water purificators. The shade opening up to allow the bright sunlight into the room is similar to that that occurs when carbon, redox or an ozonator is employed periodically.
This comes at a price as stress to certain corals may bring about bleaching or tissue loss which ultimately may lead to the death of the coral or clam. Often times corals and clams will adapt to the yellowish color of the water and the reduced amount of blue wavelength spectrum light that is used most efficiently by zooxanthellae for photosynthesis. When we create crystal clear colorless water after having turbidity for so long, we are altering light wavelength and all of the sudden bringing on an influx of the blue, violet and ultra violet rays that were not as dramatic with CDOM in the water. I should also stress that water changes will also reduce the amount of turbidity and the light alteration as well.
If you plan on using carbon or other means of replicating pristine clear water, then it is advisable to do it all the time. The maintenance of a nutrient poor water is beneficial to stony corals reef aquariums, though some nitrates in the water are advantageous and will be used by filter feeders, soft corals, clams and even stony corals to some extent.
Once again, a lot of the successes or failures we endure in the aquarium hobby are direct result of instability. Temperature, dissolved organics, salinity, alkalinity and pH all play a profound role in the water quality and quality of life for our fish and other livestock. Decisions need to be made regarding the best case scenario for you, your budget and time dedicated to ensuring the best parameters for your livestock. If you plan to use carbon, redox or an ozonator, I would use it all the time to ensure that conditions are as stable as possible.
Such a beautiful and rewarding hobby that it is crucial that we offer our livestock the best environment that we can and in doing so, we will be better able to enjoy our aquariums to the fullest without sacrificing anything.