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8.3 CARBON DIOXIDE:
CO2 is a gas that mixes with the water very easily to form carbonic acid, and is available in the tank, either in free or in bound form. The more free CO2 is present or injected, the more the pH will be affected downwards. Too much CO2 can, therefore, be harmful. Because the effects of carbon dioxide, and the resulting carbonic acid, can be neutralized by the aquarium water's buffer (we have called it the carbonate hardness), maintaining a high dKH level is important as we have already discussed in another section.
Carbon dioxide is necessary for photosynthesis by all green algae, especially symbiotic Zooxanthellae living inside the tissues of your corals and invertebrates. Photosynthesis takes place in the presence of light, more so when strong light is available. Just think for a minute about the amount of light that is available to such algae on the reef, day in day out, except for a small number of days of stormy or overcast weather. The levels and amount of lighting over a natural reef always far exceed what the average hobbyist normally provides.
If only a small amount of light is provided to the reef tank, photosynthesis will be low and the amount of carbon dioxide dissolved in the water may be sufficient for it to take place at a low level. Such carbon dioxide enters the water as a by-product of metabolism, fish and invertebrate respiration, and from the air around the tank.
As you increase the amount of light - and over a reef tank you should, especially if you are trying to recreate the natural environment - the natural amount of CO2 available in the water may be too low for proper photosynthesis to take place. Adding supplemental carbon dioxide may then become necessary. This can be done either manually, or by using an automated injection system, as we have seen in another chapter already. In most tanks the manual injection will work fine.
Because the appearance of your corals greatly depends on the amount of nutrients they receive and can absorb from the water, light intensity becomes an important limiting factor. If you provide low levels of lighting, photosynthesis will be low and your corals will suffer. If you provide high lighting, but you do not provide enough carbon dioxide, your corals will suffer as well. Their appearance is directly related to the nutrient amounts available to them. Limiting one nutrient, in this case carbon dioxide, is not recommended when what you want is for your corals to look healthy and vibrant. Although lighting is a prominent part of this natural cycle, light is not the nutrient, light is the catalyst for the process to take place efficiently.
Because photosynthesis is a process whereby macro-algae take up carbon dioxide from the water and produce oxygen as a by-product, ensuring that photosynthesis takes place in the tank has the added benefit that oxygen levels will be increased in aquariums with good algal growth.
This process can, in fact, be observed. When small streams of very tiny bubbles rise from algae towards the surface, oxygen is, in fact, being released. Some of this oxygen dissolves in the water, and increases the quality of the environment that your aquarium is. It has also been suggested that this type of oxygen dissolves three times faster than regular atmospheric oxygen, making it perhaps the best manner in which to maximize the aquarium's dissolved oxygen level.
Testing for carbon dioxide is not as easy as most hobbyists would like, because the chemicals used do not give easy to interpret results, or are affected by the high pH of the tank's water. I personally never test for carbon dioxide, but I always make sure that my tank's carbonate hardness is high. When such is the case, and you inject carbon dioxide into the water as well, its level at a pH of around 8.00 will be between 3 and 4 mg/l. Since that is the value that we should strive for, no direct testing for carbon dioxide is necessary.
Read the section on carbonate hardness in 8.7 carefully, as the use of carbon dioxide and the level of the carbonate hardness are very closely interrelated. You must understand that relationship, and feel safe using CO2, as knowing what you are doing when using CO2 puts you in the driver's seat, not the opposite. "You" should always be in control, not the tank, or the instruments and other equipment used to run it.
8.4 PHOSPHATES:
Not identified as a source of problems until perhaps 1985, phosphates are finally being recognized as one of the reasons for the frequent micro-algae outbreaks and blooms in reef, and also in other types of fish tanks. Thiel (1985 and 1988) suggests that their level should be below 1 ppm. Since then he has changed his recommendation to a level 20 times lower: 0.05 ppm. This rather substantial change is based on further experience with adding phosphate based compounds to reef tanks and observing the effect of ever increasing levels on corals and invertebrates (Thiel, Lab notes 1986-1990).
Thiel's research was a continuation of experiments conducted on freshwater tanks by several German plant experts, but had not been tried on marine reef tanks until then. All his experiments at levels higher than 0.1 ppm led to severe micro-algae problems in the tanks the tests were performed on, and result in the new recommendation of 0.05 ppm to a maximum of 0.1 ppm of phosphate for the reef aquarium.Phosphates enter the aquarium in many insidious ways. Many are deceptive and subtle, often ways that you do not even think about or suspect. Case in point: the water you use to top-off the tank, the water you use to change water in the tank, the activated carbon you use, KH buffers you my be adding, food that you administer, additives that are dispensed, the salt itself that you use, leachings from rocks you place in the tank, pH altering compounds, mineralization of organic phosphate produced in the tank, and so on. The manner in which this occurs is actually baffling, often because you do not, and have no reason, to suspect products that are sold for use in reef aquariums by reputable companies.
The only way to protect yourself, and your tank, is to test all your additives and supplements, the salt and the activated carbon you use, and anything else used before adding it to the tank. Test especially the salt, the activated carbon, and the water. My recommendation is that you change brands if they add any phosphates to your tank. Indeed, why add compounds to the water that you will spend time and energy removing, at sometimes great expense, when you can prevent adding them to begin with and avoid the problems associated with phosphate altogether?
Of course, phosphate is a required nutrient of all macro-algae that grow in your tank. Advertising therefore suggests that if it is contained in your salt or water, all you are doing is providing a required nutrient for those algae and for other lifeforms in the tank. Deceptive, because phosphate is always present in your tank in small and sufficient quantities anyway, mostly as a result of the mineralization of organic phosphates that occur as a by-product of protein and other organic compounds also present in the water. Why would you want to add more of something that is already available to the lifeforms that need it in sufficient quantity, and risk micro-algal blooms or outbreaks in the process?
Always keep phosphate levels as low as you can. Use Poly Filters from Poly Bio Marine Inc, water changes, and other chemical filtering compounds to remove excess PO4 from your tank. Keeping phosphates low should be high on your list of priorities.
Water changes are the recommended way to go if your levels are now high. After you have brought them down to the <1ppm range, rely on Poly Filters to bring them down even further and keep them low.
I have yet to come across another compound that will lower them safely, but am convinced that some will appear. The hobby evolves all the time, and phosphate removing and lowering products will be offered for certain at some point.
Some hobbyists resort to the use of Ferric chloride, a very dark powder or crystals, to lower phosphates. Tests on water that contained phosphate levels of 2.5 ppm show that after a few hours the phosphate level is actually down to close to zero, and that a floc, a sludge like material, has built up on the bottom of the container used.
Using the additive in aquarium conditions presents a problem: the floc is dispersed and ends up clouding the water for several hours, especially if a fair amount of Ferric chloride is used. Trapping the floc in micron filters is not an ideal solution either, because the cartridge used to do so plugs up rather rapidly requiring its frequent replacement. Such cartridges can cost in excess of $5.00 a piece, even when bought in quantities!
Both the pH and the redox potential are affected downwards, but only for short amounts of time when the Ferric chloride is added to a large amount of circulating water. This would be the case in aquarium conditions. No data on the long term use of this practice has been studied to my knowledge. If you decide to experiment with Ferric chloride, be careful with the quantities used, and do so on a tank that is not your pride and joy. Use it on another tank. More information will hopefully become available as time goes on. We are continuing our testing and will make whatever results we find of interest to the hobbyist available in Marine Reef, the Newsletter we publish.
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