It is more likely that the reef aquarist will be involved in supplementation, though this is not exclusively so.
In order to achieve a successful marine aquarium of any type seawater quality is very important. Another way of putting it is that for the livestock to thrive the seawater has to meet their needs. Seawater parameters also need to be stable.
The question of salt can be squeezed in here – is this supplementation? Well, perhaps not in the strict sense but anyway… The general practice in the hobby is to measure salt by checking specific gravity (SG) with a hydrometer. The usual range is 1.022 to 1.025 for a fish only system, and 1.024 or 1.025 for a reef. SG has a habit of reducing over time and this is because of salt creep etc. The aquarist no doubt keeps the seawater level topped up with freshwater (preferably reverse osmosis) and checks the SG weekly. If the SG has reduced then it is a simple matter to increase the amount of dry salt that is added for the next routine seawater change.
Some aquarists supplement general minor trace elements. This is done because these trace elements, or some of them, are probably used by livestock and are also removed by protein skimming and activated carbon. Generally, a marine aquarium should not be without a protein skimmer and so this one negative has to be put up with. Similarly there could be a case for the use of activated carbon, though its continuous use is not usually necessary. Supplementing trace elements is a hit and miss affair, the aquarist usually goes by the instructions on the bottle relative to the net gallonage of the system. There doesn’t seem to be any harm done by this, though it generally contravenes the advice ‘Don’t add anything that can’t be tested for’. The aquarist should be aware of the condition of the seawater. A better way of dealing with general trace elements, in my opinion anyway, is to carry out routine seawater changes. The new seawater will contain trace elements and though those lost may not be totally replaced, they will be at least partially and this seems to be sufficient. I have relied on routine seawater changes in this way for years and heavily stocked coral reefs have not suffered.
What is the major supplement used? A fair guess would be calcium particularly with hard coral reefs, as these SPS coral types (SPS = small polyp stony) demand good calcium levels. The usual level maintained for a hard coral reef is from 420ppm (parts per million) to 450ppm, though some aquarists maintain levels as high as 480ppm. Soft coral reefs are fine as low as 400ppm though perhaps 420ppm is better. The aquarist, if testing is regularly done and a note of calcium presence is made, will be able to see the trend. The trend is down and over a period of time the loss can be seen. This enables the aquarist to supplement reasonably accurately. There are two major ways to supplement, the first being the commercially available bottle and the second automation. Which is chosen depends on the calcium demand and the size of the aquarium. In a soft coral aquarium for example, particularly if the aquarium is not large, a commercial application should suffice if routine seawater changes alone don’t. The supplement is added to the seawater in accordance with the manufacturer’s recommendations and in a quantity relevant to the demand. The procedure is very straightforward. The second way is to automate the supplementation by using for example a calcium reactor. This makes the process continuous and probably more favourable as the ‘ups and downs’ in the calcium level are less. Some time has to be spent in very carefully adjusting the seawater drip rate and also ensuring that gas injection is correct. The other requirement is to ensure that the calcium rich media is still present in enough usable quantity.
Whether the calcium addition in manual or automated the need to test is not removed. If the aquarist can see a repetition of the calcium requirement because a notebook has been used to jot down test results over time, then testing can be reduced in frequency¸ but nevertheless still needs to be done.
Another measure that needs to be known particularly with a reef system is alkalinity. Alkalinity is the measure of how much bicarbonate and to a lesser extent carbonate is present in the seawater providing resistance to downward changes in pH. It is sometimes called carbonate hardness or buffer capacity. A complete description of alkalinity will not be gone into, but from the foregoing it can be seen that it is important, the pH of seawater needs to be stable and in the correct range. So the reef aquarist needs to test and note the reading. Again, the trend for alkalinity in an aquarium is downward. Routine seawater changes will assist in the maintenance of the alkalinity level, but supplementation is often also required. Natural seawater has an alkalinity level of around 2.5meq/L. (Don’t worry about the unit measure of alkalinity, test kits give tables and usually conversions to other measures. The unit meq/L is only being used for demonstration. The measure often used otherwise is dKH, and to obtain this simply multiply the meq/L figure by 2.8.) The seas and oceans have vast reserves but in the comparatively diminutive aquarium with a relatively higher bio load it is usual to maintain a higher alkalinity level of between 3 to 4.5meq/L, though 4.0meq/L seems a good measure. Again, if tests have been completed over time and a note made the trend of the aquarium can be seen, permitting the aquarist to know how much needs to be supplemented. Supplementation can be manual using additives that are commercially available, a very straightforward process. Another way is to use sodium bicarbonate (baking soda), use about one teaspoonful per 25 gallons of seawater and add to the sump or another area away from corals (mix the powder in some seawater before adding it). If the aquarist uses a two part alkalinity/calcium additive or uses Kalkwasser there could be no need for further alkalinity supplementation. Tests will give the answer.
There are other supplements available, but there is more controversy over these. For example, iodine is said to be particularly beneficial to soft corals and of benefit to all types. Iodine is available commercially and should be added strictly according to the instructions. Only a small amount is needed as required iodine levels are very low. As far as I am aware there isn’t any scientific proof that iodine addition is of any great benefit to the reef livestock, though there are many aquarists who do add it and state that it is of use. With this state of affairs it would seem reasonable to add it, remembering that some will be gained from routine seawater changes. Iodine can be tested for.
Magnesium could be another addition used by the aquarist. Sometimes the dry salt mix itself falls short of the desired level though this is probably uncommon. A check of the level present in the aquarium seawater should be made and a decision based on that.
There are other little bottles that can sometimes be found in aquarium stores, such as molybdenum, bromide, fluoride and vanadium. Sometimes the bottle could contain more than one. Whether there is a real need for supplements of this type is a basis for argument. All I can say is there are many aquarists with lovely successful aquariums that have never used them. Also, routine seawater changes will replace necessary elements at least to an extent.
The main point that needs to be remembered is that ‘magic bottles’ do not bring success, the design and maintenance of the aquarium is the main foundation for this. Maintenance includes testing of the seawater and ensuring that any known necessary elements are present in amounts that are required by the livestock. Overdosing can be very detrimental, so the aquarist has to know the additive quantity actually required without guesswork, which means seawater testing. This testing can be reduced in time if the aquarist keeps a note of test results and aquarium trends can be seen, however testing still needs to be done.
Another point worth mentioning is that if any desired level is found to be markedly deficient supplementing to regain the correct level should not be done quickly. Stability is a requirement already mentioned, so if a larger change is required it should be done slowly in small steps.
‘High quality seawater’ is generally accepted as the number one requirement in any type of marine system. This high quality is sometimes simply interpreted as a lack of nitrates and phosphates which is correct up to a point. Particularly in a reef system, the presence of elements in sufficient amounts to meet the needs of livestock is also important.