Carbon dioxide transfers to the water at the air and water interface, and also inside the biological filter chamber. In addition, carbon dioxide is produced in the tank, by the tank inhabitants, as a by-product of respiration and metabolism.

Carbon dioxide in moderate amounts is certainly not noxious. It is, in fact, beneficial. Indeed, it is necessary for photosynthesis to take place. Zooxanthellae, the symbiotic algae that many corals depend on for their survival and well being, require carbon dioxide as well. So do all macro-algae. Zooxanthellae that do not obtain their required amount of carbon dioxide cannot photosynthesize efficiently, and as a result, your corals do not receive as much nutrients as they could. This will affect their appearance and survival rates.

Carbon dioxide itself is not noxious. The problem occurs when hobbyists decide to inject carbon dioxide into the water in some form or another, because not enough of it is present in the tank, but do so without really understanding, from a chemical point, what is really happening when such is done.

To safely inject carbon dioxide you must read the passage fertilization and carbonate hardness, earlier in this book very carefully, and make sure that you understand what is going on. If not, call us, or anyone else knowledgeable about CO2.

Briefly, when carbon dioxide mixes with water, it produces a weak acid called carbonic acid. This acid, as any other acid, will have a depressing effect on the pH, unless the carbonate hardness (the buffer in this case) of the water is able to neutralize the effects of the acidity. The carbonate hardness of the water must always be above 12 dKH when you inject CO2, and the amount of carbon dioxide added must be such that it does not affect the pH of the tank by more than a maximum of 0.2 pH. Adding carbon dioxide is, therefore, a process that you must monitor for a while when you first set it up, to ensure that nothing is happening to the system because too much CO2 is being injected, too rapidly, and has lowered the pH dangerously.

As your system becomes more sophisticated in its holistic control of all parameters, equipment is often used that you are not as familiar with as you are with more traditional types of filters and controls. You must, for the sake of the aquarium and its inhabitants, take the time to understand these instruments and methods to prevent you from making costly mistakes. Many manufacturers will help you over the phone in setting up their products. Take advantage of these offers. Call them before setting up the equipment if you are not sure how to do so. Don't do it after you made the mistakes. This remark applies especially to setting up carbon dioxide injection systems, especially manual injection ones.

Often hobbyists are worried about the effects of nicotine and tar that enter the air as a by-product of cigarette, pipe and cigar smoking, and transfer to the water, as we have seen in the airborne pollution section.

The dangers associated with such compounds are real, but are completely neutralized by the use of Poly Filters and/or activated carbon. They should not be a cause for concern if chemical filtration is used, especially if you also pre-filter the air that your pump blows into the filter and into the water.

Cigarette butts thrown in your tank, for example while you have guests, will however do considerable damage.

Iron is a required fertilization compound by those hobbyists interested in growing macro-algae such as Caulerpa, and other species of larger green algae. Iron can however be toxic if too much of it is added to the tank.

Iron is also not the only element that such macro-algae require. A complete fertilizer needs to contain much more than iron. We are covering algae in more depth in a later chapter.

Maximum recommended levels are 0.05 ppm to 0.1 ppm of iron as measured with standard aquarium tests. Too high levels, e.g. 0.5 ppm can become dangerous if maintained for too long, not for fish, but for corals and invertebrates. Evidence exists (Thiel, 1988) that 1.5 ppm first affects Heteractis malu adversely, and results in its loss in a period of about 3 weeks, if those levels are maintained by the addition of chelated iron salts. Use iron responsibly and you will not have any problems with corals and other tank life forms.

Permanganates are used to improve the water quality in those cases where the organic load has increased so much, that the hobbyist is at loss about what to do to improve the quality of the water quickly and effectively, using more traditional methods.

Permanganates are very strong oxidizers and must be used with care. Adding too much of any one of them will raise the redox potential very quickly, and to levels that are either dangerous, or fatal to many forms of life that you have in your aquarium. Follow the manufacturer's instructions very carefully, and you will not have any difficulties in improving the quality of the water.

Permanganates are not meant to be used continuously. You should only use on an as required basis, and for short periods of time, perhaps a few days in a row. Perform a large water change after the treatment period is over; 20 to 25 percent is not unusual. Make sure that the water and the salt used conform to the parameters already outlined earlier:

• They should not contain nitrates and phosphates.
• They should not add other undesirable compounds.
• Ideally you should chemically filter the water thoroughly before using it for water changes or top-offs.

This very toxic compound mixes with the water very easily. Conditions that are propitious to its formation must be avoided at all cost, if you are planning to run a successful reef aquarium. Hydrogen sulfide forms when decay occurs in areas where oxygen is very low, or non existent. Because it contains sulfur, a foul smelling compound, one can detect the presence of H2S at very low concentrations.

Hydrogen sulfide appears in tanks because the tank's water contains both inorganic sulfate (a great deal of it), and organic sulfur from the decomposition of protein. Small amounts of hydrogen sulfide will be re-oxidized to harmless substances in tanks that have high dissolved oxygen levels and good water circulation in all areas of the tank. As a result, they are no cause for concern.

In tanks with low levels of dissolved oxygen and in tanks with inefficient water circulation, for example behind rocks, hydrogen sulfide may not be re-oxidized or may be produced in larger amounts. This may result in a depressed water quality condition that cannot, seemingly, not be attributed to any particular cause. Higher temperatures increase the sensitivity of all life forms to hydrogen sulfide.

Rather than having to cope with its presence, the hobbyist should set up the aquarium in such a fashion that hydrogen sulfide is not a cause for concern. Maintaining high levels of D.O., combined with a good water flow throughout the aquarium, is the recommended method that will not fail you.

If you use one, pay particular attention to your denitrating unit. Make sure that it is operating correctly and that no hydrogen sulfide is leaching slowly, and continuously, into your tank. Denitrators are very efficient at removing nitrate from the water, especially if you use them with the required nutrients (not everyone does, unfortunately), but you must monitor their operation regularly. Alternatively, acquire a unit that is of the second generation type, larger, and allowing for a more rapid flow of water, making it less likely to stop and become totally anaerobic or slow down considerably and go somewhat anaerobic (not totally, but in some areas of the denitrator).

Pay attention as well to all your mechanical filters. Clean them regularly. Once a week is a minimum. Mechanical filters that work efficiently obviously trap dirt and particulate matter. As the filter traps more and more such matter, some areas of the filter will plug, become trapped with so much dirt, that no water can circulate through it anymore. Water bypasses such areas, and anaerobic activity which produces hydrogen sulfide will soon start. Cleaning your filters regularly, and changing the material used for mechanical filtration from time to time, will avoid this pitfall.

Be aware that mechanical filtration occurs in other areas than you may think of. You may have set up a filter that you consider your mechanical filter, and you may be cleaning that filter regularly, thinking that your practices are in line with normal recommendations. But you may overlook the fact that other filters that are installed function as a mechanical filter as well.

The following should guide you in deciding what you need to clean regularly: any material in the tank or water circulation system that obstructs (offers resistance) to water circulation will trap dirt. Some faster than others. The former will need to be cleaned more regularly than the latter.

DLS in your biological filter, for example, is no exception but is often not considered a mechanical filter. Unfortunately DLS does trap dirt and can cause anaerobic areas within the biological chamber, the worst location to have such activity. If your roll of DLS has collapsed somewhat, getting lower and smaller, you may have a problem.

This is also the main reason for my recommendation not to use DLS in biological filters. Granted, one can prefilter the water going to the biological filter thoroughly. The fact remains however the same. The filter will still trap dirt. It will just take longer for it to happen. Give yourself peace of mind, use a plastic filtering material. You may have to spend a little more, but it is worth the effort in the long run. Believe me, cleaning a biological filter that contains DLS or a similar material is no fun and is a messy affair.

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