The accumulation of organic and inorganic acids, even CO2 as carbonic acid during night hours, can easily take its toll on an alkalinity of only 2.5 meq/L in a confined aquarium environment. To put this buffer capacity in perspective, consider that in most biological studies, such as tissue or cell culture—and reef tanks have more in common with test tube culture than the open ocean—buffers are required to be in the range of 50 - 200 meq/L. Another way to look at it: less than a single fluid ounce of commercial muriatic acid added to 50 gallons of sea water will completely consume its alkalinity at 2.5 meq/L. A buffer capacity of 2.5 meq/L is almost no buffer at all. I recommend 5 meq/L, and even this is minimal buffering. I do not recommend more, not because it would be harmful, evidence indicates otherwise, but because at greater than 5 - 6 meq/L it becomes almost impossible to maintain a calcium concentration approximating 380 mg/L. In a fish only tank (not reef), it is advisable to maintain higher alkalinity and ignore the calcium content. I do not subscribe to the notion that natural sea water is the perfect media for sea life, but it is a good starting point. We have little information on most constituents of sea water, so that to deviate from them very much tends to be experimental, but for some constituents, such as alkalinity, we have enough experience to be confident that reasonably increased alkalinity is beneficial. The same might be said for slightly lower salinity than is generally found in sea water.

Redox

Redox is another poorly understood measurement in the hobby. Redox is measured with an electrode, very much like pH is measured with an electrode. Just as electrode pH measurements are very much dependent on a properly functioning and calibrated electrode, true redox measurements are even more dependent on function and calibration of the electrode. Unfortunately, redox calibrators do not have the stability characteristic of pH calibrators. While accuracy and precision are dependent on electrode function, many hobbyists have the natural inclination to assume that digital read-outs are highly accurate, regardless of the condition of the electrode.The assumption behind redox measurements is that organics depress redox and the removal of organics raises redox. All organics are assumed to be harmful. High redox is associated with oxygenation and good water quality. In fact, redox is a measure of the ratio or equilibrium between oxidizing and reducing substances in the water. It does not address the issue of whether these oxidants or reductants are harmful or beneficial. The underlying assumption is that oxidants are good, reductants are bad. Redox measurements can be useful if they are made reliably and the aquarists is aware of what can alter measurements without necessarily reflecting a decline or improvement in water quality. The addition of strong oxidizing agents, such as ozone, peroxide, permanganate, persulfate, or hypochlorite, will produce an immediate rise in redox of themselves, and this has no particular benefit. Ultimately, these oxidants will oxidize something oxidizable and that may be of benefit, but the benefit was not reflected by the initial rise of redox from the oxidants themselves.

Likewise, the addition of reductants, such as vitamin C, other vitamins, amino acids, some nutrients, dechlorinating or ammonia removing compounds, will cause a drop of redox, but this does not reflect a decline in water quality. Even innocent fluctuations, such as pH, alkalinity, or temperature rise, will cause a drop in redox. Day or night, feeding, filtering media, water changes, all of these have innocent effects that are not faithfully reflected by redox changes. High nitrates are undesirable, yet nitrates will cause an upward swing in redox. Redox measurements are a tool. Used intelligently they can be helpful, used compulsively they can be dangerous. Provided an aquarium is well oxygenated and well maintained with water changes and some form of chemical treatment such as skimming and organic filtration, it is more likely that damage will be caused by too high a redox than by too low a redox, usually because someone feels compelled to raise redox by adding some strong oxidizing agent. Using a redox meter is a lot like investing in stocks. If you follow the normal ups and downs too closely, you will probably end up losing it all. It is very possible to maintain a successful reef aquarium without ever taking a single redox measurement.

Ozone

Another area of concern is ozone. Ozone is a very unstable triatomic form of oxygen and is a very powerful oxidizer. It is often recommended for use with skimming. In freshwater, ozone oxidizes organic material and ultimately breaks down to free diatomic molecular oxygen. In sea water, however, ozone reacts instantly (microseconds!) not only with organics, but first with iodide, bromide, and chloride ions to form hypoiodite, hypobromite, hypochlorite (bleach!), also iodine and bromine. The latter two are just as bad as chlorine. Ozone also reacts with available manganese, iron, magnesium, and even calcium ions and depletes them from solution. Ozone is non-discriminating and destroys useful amino acids, vitamins, and other deliberately added nutrients as well as the undesirable organics. Ozone cannot escape into the tank itself, being too short-lived, but its byproducts, predictable (bleach) and unpredictable (what did that unidentified organic released by that anemone incompletely break down to?) can. With all the proper caveats in place, ozone can be used safely, but is it worth it?

Phosphate

Despite rumors to the contrary, phosphate is not among the most toxic substances known to man. Phosphate is essential for all life forms, even viruses and corals. Phosphate is a major component of DNA and RNA and life cannot get very far without one or both of these. Phosphate has limited solubility in sea water, most of it precipitating naturally as magnesium and calcium phosphates, major components of detritus. Phosphate is harmless to fish and most invertebrates. Excess phosphate, greater than 0.1 - 0.2 mg/L (ppm), can interfere with the growth of some corals and promotes the proliferation of hair algae. Common sources of phosphate are seasonal peaks in municipal water supplies, the biota of the aquarium, food, and activated carbon.