The reef aquarium with hard corals ([tag-tec]SPS[/tag-tec]) is the desire of many an aquarist. The sight of pictures on the internet and in books only serves to increase that desire. With modern aquaria and equipment, plus the knowledge gained over recent years, this desire can be met, and more easily than some suspect.
It is taken as read that the need for high water quality is understood. High water quality means a proper and stable pH, between 8.0 and 8.4, nitrate less than 10 ppm (parts per million), phosphate preferably undetectable, but no more than 0.03 ppm, and ammonia and nitrite undetectable. Equipment should include a properly sized and efficient protein skimmer. Water movement, which I consider a part of [tag-tec]aquarium water quality[/tag-tec], should be vigorous and chaotic. There is also a need for strong lighting, the best of which is metal halide, supplemented by actinic T5 fluorescents. A greater number of T5 fluorescents can be used without a metal halide, as many as can be fitted into the aquarium including their reflectors. The T5’s should be an equal, or as near as possible equal, mix of marine white and actinic. However, at least in my opinion, the halide lighting is the best option.
If the reef is a mix of hard and soft corals, then parameters should be for the needs of hard corals. Soft corals will not suffer. Water quality measurements (pH, nitrate, phosphate etc) would be the same for both.
So that’s sorted then, back to additives.
Hard corals require calcium, and require it considerably more than the soft corals. Modern commercial salt mixes contain a good level of calcium, particularly those more recent ones which are specifically designed to give a high calcium reading for the [tag-tec]reef tank[/tag-tec]. The calcium level that should be maintained is 450 ppm, and should not be maintained at less than 400 ppm. (Some aquarists have the level at 480 ppm or sometimes a little higher.) This does not mean to say that the calcium reading must always remain exact at a particular level, it will of course vary to a reasonable extent. Even with regular routine water changes, a hard coral reef ‘s demand will reduce it.
So how can calcium be maintained. The first option is supplementation with commercial products. The product instructions advise how much should be used to raise the calcium reading by X, according to the net gallonage of the aquarium. All increases should be gradual, and the instructions followed. These products are suitable for a small aquarium, for instance a nano system or up to a net fifty gallons or so. The products are not cheap, however, and larger aquariums will require larger doses so other methods need to be considered. The first, and recommended method, is to purchase a calcium reactor. This is an external device where the aquarium water is passed through the device, and is exposed to a chamber containing a calcium carbonate medium. This would normally have little effect. However, carbon dioxide is also fed into the chamber, and this causes the medium to slowly dissolve. As it dissolves it releases calcium, along with other trace elements. It is an efficient way of maintaining calcium. The water flow rate and the input of carbon dioxide must be correct and controlled. The aquarist must change the medium when it appears ‘mushy’ or is nearly gone. The calcium level must also be tested at least weekly as it is important to know that the reading is that desired. If too much calcium is being produced, then the running time of the device can be reduced until correct (ie. turned off for X hours each day). There are other means of introducing calcium, for example kalkwasser (limewater). Kalkwasser has drawbacks: it should really be mixed fresh each day which is a fussy procedure, and, as it has a high pH, needs to be introduced to the display aquarium slowly and carefully. The aquarist needs to exercise care as the mix is caustic. In addition, if the calcium level in the aquarium is low, the kalkwasser may be ineffective because the amount that can be introduced to the aquarium is limited. Put too much in and the sudden pH rise could be dangerous to the reef.
Talking of calcium brings the discussion to alkalinity. This is an important parameter and should be within certain readings. These reading are 9 to 11 dKH (151.1 to 196.9 mg/l). The alkalinity of seawater is its ability to resist downward changes in pH. It has a buffering capacity. Hard corals require stability and ensuring that alkalinity is at an acceptable level greatly assists this stability. Alkalinity affects the amount of calcium (and trace elements) that can be maintained. However, if alkalinity rises too high then calcium levels that can be maintained will be lower. So, as said, alkalinity should be maintained at a reading as suggested. How is the reading maintained? Again, commercial preparations are available which contain carbonates and bicarbonates. These should be mixed and applied as per the instructions supplied and according to the net gallonage of the aquarium. Again, the commercial preparations may prove to be too expensive for large reef systems. There is an alternative, applicable to small systems as well. Purchase some ordinary baking soda (sodium bicarbonate) from a shop. If this generates too much nervousness, obtain it from a chemist. It is safe but should be dosed carefully. As there will not be any instructions for use with a marine aquarium the following is a guideline: when raising alkalinity, divide the aquarium net gallonage by 25. Add a teaspoon for each 25 gallons. So 50 gallons would need two teaspoons. Aquariums with a net gallonage lower than 25 would need to add the appropriate fraction of a teaspoon. Mix the soda in some aquarium seawater and add to the sump, or to the aquarium away from livestock. That is the full daily dose, the alkalinity level should be checked by testing before adding any more on the following day. Once the required level is reached, the aquarist will soon discover how much his/her aquarium needs to be supplemented. For alkalinity and calcium, the following link gives further information. It really relates to those who are experiencing problems, but nevertheless gives information and parameter suggestions.
Iodine is considered by many to be beneficial to corals. This often refers to the soft variety, but there is a fairly strong body of opinion that suggests hard corals will benefit as well. Iodine in natural seawater has a very low presence, 0.06 ppm. Commercial preparations are available, and if used regard must be given to the net gallonage of the aquarium and the manufacturer’s instructions as usual. There is a drawback, and this is that, as far as I know, there isn’t a test kit that will reasonably accurately check iodine levels. If that remains the case, then do not exceed the recommended dose if the aquarist must use it. Alternatively, if regular routine water changes are completed and if the corals are healthy, expanded and growing, then don’t use it.
There are all sorts of trace element additives available to the aquarist. For example, strontium, molybdenum and iron. Other available magic bottles are said to contain a mix of essential elements. I am not a scientist. Nevertheless, the books I have read by very knowledgeable and up to date authors suggest that there is no scientifically supported need for these to be supplemented, therefore it must be that any benefit suggested from their use is anecdotal. I do not, and am not qualified, to challenge their use. However, I would suggest doing regular routine water changes using a high quality mix. There are several good preparations on the market nowadays. These will introduce trace elements to the aquarium seawater. Observation of the corals will advise the aquarist accurately: if the corals are expanded and healthy then.fine