Cyanide is known to hobbyists as the controversial chemical used in catching fish, to stun them and make them easy to trap in nets by divers around reefs in the Indo-Pacific region. Although technically illegal, it is still being used widely according to several sources, not the least of which is the International Marine Association. It is a practice that should be stopped, regardless of whether it does damage to the fish or not. It is a practice that if continued, will destroy the reefs in the long run. Steve Robinson of Cortez Handcaught has been fighting for this cause for years, and should get all involved's support. Buy from dealers who will guarantee hand-caught stock.

The two main dangers associated with cyanide, irrespective of how it entered the water, is that it affects the animal's oxygen metabolism, and that at high pH levels cyanide will combine with hydrogen to form hydrocyanic acid, which is very toxic to invertebrates and fish.

Cyanide is destroyed by ozone, permanganates and chlorine. The latter cannot be used in aquariums, but the former are. Many hobbyists now use ozone in combination with protein skimmers, and sometimes with ozone reactors, greatly reducing the danger. Frequent water changing and using chemical filters are other suggested ways of ensuring that this highly toxic compound does not slowly poison your corals, fish and other lifeforms.

AS A SIDE NOTE: vitamins are sometimes added in great quantities to supplement possible deficiencies in the food, or to make up for the deficiencies that occur as a result of various forms of filtration. Some hobbyists even add supplemental B12 vitamins. This is fine, as long as the hydroxocobalamin form is used, and not the cyanocobalamin variety. Adding vitamins is strongly recommended for those hobbyists who also use large amounts of ozone to clean up the water and increase the redox potential of the water. Mix it with the food, or add them separately, but make sure you use a high quality brand. Vita Chem, Coralife, Marineland and TAT are all recommended.

Mercury is an extremely poisonous compound. It is not a problem as such, as under normal circumstances you will not find it in your water supply, but mercury can become a problem if you are using an older style thermometer and break it by accident in the aquarium. Indeed, such thermometers contain mercury, a silvery, shiny looking metal.

Should this happen, you must try to remove the mercury immediately, or make large water changes. Because mercury "beads", it breaks up in even smaller beads, you must use a siphon hose and hold it over the beads to remove them. Use ¼" inch I.D. hose to do so, and do it immediately. Mercury poisoning is fatal to all invertebrates, fish, and whatever else you may be keeping in the tank. Be very careful with old thermometers around the aquarium.

Phenolic compounds are of organic nature, and will appear as intermediate breakdown compounds of many of the chemical reactions that take place in your aquarium. Phenols are toxic, and that toxicity increases with higher salinities and lower redox potentials. The use of ozone will, however, rid the tank of the danger.

Additionally, chemical filtration, using highly activated carbon of good quality (e.g. pelleted coconut shell), or especially Poly Filters, will remove phenol, and more complex types of phenols from the water as well.

Another series of compounds that are not only very toxic and that, in addition, are taken up by your corals and invertebrates quickly. Sanders (1973) recommends the use of a properly sized protein skimmer, ozone, and good maintenance practices to avoid that these esters rise to dangerous levels (of only a few micrograms).

Of course this must be combined with regular partial water changes, and good general maintenance practices (see elsewhere in this book for more recommendation on changing water and a later chapter for maintenance and husbandry).

Lead does not serve any known function in animal and plant life, and is extremely toxic to all forms of life kept in reef and other aquariums. Nowadays lead poisoning is a highly unlikely event, but water supplies, in old houses with lead pipes, may need to be checked carefully for lead before that water is used.

Another often overlooked source of lead in the water, are leachings from painted decorations that are sometimes placed in tanks. Mistrust anything that is painted, varnished, or otherwise coated, unless you know for sure which compound was used.

The only occurrence of lead in an aquarium that I have been exposed to myself, was in an aquarium where a lead pencil had been dropped and left for a long time. It only became apparent when the tank was eventually taken down, and the long pencil lead was found in the gravel, the wood around it having totally decomposed.

All pesticides are toxic to invertebrates, and in certain concentrations they become very toxic to fish as well. You do not, of course, add such compounds intentionally. They enter the tank's water as compounds dissolved in either water mains, but more often so in well water. This is yet another reason why well water should always be treated chemically before it is used and added to an aquarium. Use Poly Filters from Poly Bio Marine Inc. (best) or a very good quality activated carbon (as already indicated make sure that it is activated and that it does not add phosphates to the water).

Many toxic compounds can enter the aquarium water from the surrounding air and, if they are not removed by some form of filtration (chemical) or regular partial water changes, they will build up to levels that may be just noxious enough to keep your tank in a drab looking state, or in a depressing looking shape.

The quantities present or the types of pollutants may not be of a toxicity level that kills fish and invertebrates quickly, and thus hobbyists do not pay any attention to them. In fact, in most cases hobbyists do not even suspect their presence.

It is, usually, only after hobbyists have exhausted all other methods and possible causes of pollution, and are at a total loss to understand what is going on in their tanks, that someone may suggest airborne pollutants. This is because when you have tried every method recommended by books and talked to pet stores in your area, you may start asking questions by calling around to manufacturers, reef specialists and so on. The latter may have a wider experience with this form of pollution.

These airborne compounds, which include fumes from paint, compounds used around the house to kill flies and insects and such, kitchen fumes, nicotine from smoking, etc. can all be removed easily from the water as long as adequate chemical filtration is used. Again, Poly Filters or very good quality activated carbon are the answer.

Besides entering at the air and water interface, these compounds will also enter the water because your air pump pushes ambient air into the tank, or into the filter, or both. If that air contains pollutants, the latter will end up in the water.

Because most of these pollutants do not cause instantaneous reactions, they are often overlooked. In fact, it does not even occur to most hobbyists that the air in the room where the filter and/or the aquarium are placed can be a source of problems.

In order to avoid them you may wish to filter the air that goes into your filter, or into your ozonizer, through activated carbon first. Alternatively, do as I do and fill an old air dryer with cut up pieces of Poly Filter. It restricts the air less, and does not remove oxygen from the air (which makes your ozonizer work better).

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