Calcium [Ca] - Required addition. A range of 400 - 450 ppm Ca++ is recommended. The preferred method is the usage of Kalkwasser [Lime water] for all evaporation make up water. The use of Calcium Chloride (CaC12) is known to cause problems with alkalinity ( provable by balancing the relevant chemical reactions occurring in the tank when CaC12 is added). Still, CaC12 is occasionally useful to repair serious Ca++ deficits.

Calcium - The efficacy of chelated calcium products available for the reef aquaria is questionable. To the best of our knowledge, there exists no scientific evidence indicating that chelated calcium is especially available to corals and other CaC03 depositing invertebrates. Nothing is known about the uptake of chelated calcium by corals. And most importantly, there exists no evidence showing that chelated calcium products support stony coral growth rates in excess of, or even comparable to growth rates documented in aquaria where calcium is supplied as aqueous Ca (OH)2 [Kalkwasser].

Chelated calcium products also interfere with the ability to measure actual calcium levels in the aquarium. In particular, chelated calcium cannot be measured by any kit which uses EDTA titration, including the highly recommended HACH kit. Some people find the SeaChem kit, which does measure chelated calcium, to be impossible to read with any accuracy. Until such time as vendors supplying chelated calcium products make available well conceived, carefully documented uptake and growth studies with their products, or the same experiments are performed and published by third parties, regard the use of chelated calcium products in the reef aquarium to be experimental at best especially when Kalkwasser and other non chelated calcium sources are known to support the growth and even reproduction of stony corals in the home reef aquarium.

Other additives, especially the commercial "secret formula" mixtures are more controversial. Some people report good results from some of them other people report disaster or no effect. Experiment cautiously with them if desired.

Alkalinity - Alkalinity is a measure of the acid buffering capacity of a solution. That is, it is a measure of the ability of a solution to resist a decrease in pH when acids are added. Since the acids are normally produced by the biological action of the reef tank contents, alkalinity in closed system has a natural tendency to go down. Additives are used to keep it at a proper level.

Correct alkalinity levels allow hard corals and coralline algae to properly secrete new skeletal material. When alkalinity levels drop, the carbonate ions needed are not available and the process slows or stops.

Alkalinity is measured in one of three units: milliquivalents per liter ( meq/l ), German degrees of hardness ( dKH ) or parts per million of calcium carbonate ( ppm CaC03 ). Any of the units may be used but dKH is most commonly used in the aquarium hobby and meq/l is used in literature. The conversion for the three units is:

Alkalinity is often confused with carbonate hardness since both participate in acid neutralization and test kits may express both in either of the three units. However, carbonate hardness is technically a measure of only the carbonate species in equilibrium, whereas alkalinity measures the total acid binding ions present. Which may include sulfates, hydroxides, borate's and others, in addition to carbonates. In natural sea water, carbonates make up 96% of the alkalinity so equating alkalinity with carbonate hardness isn't too far off.

Some recommended test kits for alkalinity are the SeaTest kit and the LaMotte kit. The SeaTest kit is very inexpensive and is one of the few SeaTest kits suitable for reef use. The SeaTest kit measures in divisions of 0.5 meq/l or, if the same amount of solution is doubled, 0.25 meq/l. The SeaTest kit uses titration in which the acid and indicator are included in the same reagent. The LaMotte kit is a little more expensive, though still fairly cheap, and is more accurate. The unit of titration is 4 ppm CaC03 although in practice, one drop from the titration tube may be up to twice this amount making the resolution about 0.15 meq/l. The LaMotte kit has a separate indicator tablet and acid reagent which is a nice feature.

Calcium levels of natural surface sea water are around 420 ppm Ca++ In a running reef tank you will notice, sometimes dramatic, calcium depletion. Calcium addition in some form is essential. A calcium level above 400 ppm is required and a range of 400 - 450 ppm Ca++ is recommended.

Nitrates themselves may not be a problem but serve as an easily measured indicator of general water quality. Many hard to test for compounds like dissolved organics tend to have levels that correlate well with nitrate levels in typical tanks. Different authors cite varying upper nitrate values permissible. No higher than 5 ppm NO3- is a good number with less than 0.25 ppm recommended. Unpolluted sea water has nitrate values below detectable levels of test kits, so "unmeasurable" is the goal to strive for.

Most test kits measure nitrate-nitrogen. Do not forget to multiply by 4.4 to get the ionic nitrate reading. LaMotte makes a nitrate test kit that will measure down to 0.25 ppm NO3-N. Hach makes one good to 0.02 ppm N03-N, about 10x more sensitive, but you must be sure to order the saltwater reagents. They will only sell you the saltwater reagents in addition to the regular kit with freshwater reagents, not in place of them, which is annoying. This makes the Hach kit about twice as expensive in the end as the LaMotte kit but the 10x increase in performance makes this more acceptable.

1.025 is recommended for reef tanks. Note that virtually all hydrometers are calibrated for measurement at a temperature of 60 F. Included below is a short table of temperature adjustments. Add the value shown to your hydrometer reading to get an accurate reading.

If the hydrometer reading is at 1.0235 at 80 F, the actual Specific Gravity is 1.0235 + 0.0024 = 1.0259.