Saltwater Fish & Coral

salt water fish
A responsible aquarist will research and make important decisions before setting up a tank, ensuring the fish, invertebrates, and plants will be able to live long and healthy lives. Maintaining good water quality is the single most important thing that aquarium owners can do to ensure the health of their fish. Poor water quality is probably responsible for more aquarium fish deaths than any other factor.

Optimal Marine Aquarium Water Parameters:


Calcium (380-450 ppm)

Calcium is what all of your coral and inverts need to stay healthy and grow. The calcium in your water is rapidly used up by the growth of your corals, which is why it’s very important to add a calcium supplement regularly (every few days, to keep levels between 380-450 ppm). We carry a number of good options, such as Brightwell Reef code A & B, SeaChem Fusion 1 & 2, Kalkwasser, and SeaChem Powder Calcium.

Keeping your calcium levels balanced is one of the most essential aspects of coral reef aquarium husbandry. If your aquarium’s calcium levels need to be replenished significantly, I recommend using a powder Calcium supplement to avoid raising your alkalinity too much (Reef advanced calcium powder works well for this). Coral Skeletons are comprised of calcium carbonate, which SeaChem Reef Advanced Calcium Powder provides.

Alkalinity, also known as hardness

Similar to calcium, alkalinity also helps your Corals grow. Alkalinity levels are often a surrogate measure for bicarbonate, which corals convert into carbonate(for their calcium carbonate skeleton).

Aquariums that are not supplemented will experience rapid depletion of alkalinity, so it’s recommended to maintain your alkalinity levels at or slightly above normal seawater (7-11dKH). Alkalinity levels will also vary depending on the aquarists goals (for example, if rapid skeletal growth is desired than higher alkalinity levels should be targeted— cautiously, to avoid depressing the calcium levels and creating undesirable consequences).

“If left unchecked, the alkalinity drops below a critical level and pH begins to fluctuate more wildly than is normally suggested (a daily pH shift of +/-0.2 is normal in marine aquaria), causing stress to livestock. Alkalinity is also depleted by reef-building organisms during the production of aragonite (~60% carbonates by weight), and is therefore very important for their rapid growth. Maintaining the alkalinity in marine aquaria between 7 – 12 dKH (2.5 – 4.3 meq/L) will generally maintain pH within the desired range.” (Brightwell Alkalin 8.3 Powder)


is your concentration of salt in your water, often reported through specific gravity (which is unitless) or salinity (in units of ppt, parts per thousand). Different tools test for Salinity using different units of measurement. Hydrometers use specific gravity, refractometers use refractive index, and conductivity probes use conductivity. The salinity of natural ocean water is 35ppt, corresponding to 1.0264 and 53mS/cm. At Coastal Reef we keep our saltwater between 1.024 and 1.026.


Optimally around 80◦, but ok anywhere from 76-83 degrees Fahrenheit.

“Temperature impacts reef aquarium inhabitants in a variety of ways. First and foremost, the animals’ metabolic rates rise as temperature rises. They may consequently use more oxygen, carbon dioxide, nutrients, calcium and alkalinity at higher temperatures. This higher metabolic rate can also increase both their growth rate and waste production at higher temperatures.

Another important impact of temperature is on the chemical aspects of the aquarium. The solubility of dissolved gases such as oxygen and carbon dioxide, for example, changes with temperature. Oxygen, in particular, can be a concern because it is less soluble at higher temperature.

So what does this imply for aquarists?

In most instances, trying to match the natural environment in a reef aquarium is a worthy goal. Temperature may, however, be a parameter that requires accounting for the practical considerations of a small closed system. Looking to the ocean as a guide for setting temperatures in reef aquaria may present complications, because corals grow in such a wide range of temperatures. Nevertheless, Ron Shimek has shown in a previous article that the greatest variety of corals are found in water whose average temperature is about 83-86° F.

Reef aquaria do, however, have limitations that may make their optimal temperature somewhat lower. During normal functioning of a reef aquarium, the oxygen level and the metabolic rate of the aquarium inhabitants are not often important issues. During a crisis such as a power failure, however, the dissolved oxygen can be rapidly used up. Lower temperatures not only allow a higher oxygen level before an emergency, but will also slow the consumption of that oxygen by slowing the metabolism of the aquarium’s inhabitants. The production of ammonia as organisms begin to die may also be slower at lower temperatures. For reasons such as this, one may choose to strike a practical balance between temperatures that are too high (even if corals normally thrive in the ocean at those temperatures), and those that are too low. Although average reef temperatures in maximal diversity areas (i.e. coral triangle centered Indonesia,) these areas are also often subject to significant mixing. In fact, the cooler reefs, ( i..e. open Pacific reefs) are often more stable at lower temperatures due to oceanic exchange but are less tolerant to bleaching and other temperature related perturbations.

All things considered, those natural guidelines leave a fairly wide range of acceptable temperatures. I keep my aquarium at about 80-81° F year-round. I am actually more inclined to keep the aquarium cooler in the summer, when a power failure would most likely warm the aquarium, and higher in winter, when a power failure would most likely cool it.

All things considered, I recommend temperatures in the range of 76-83° F unless there is a very clear reason to keep it outside that range.” (, Reef Aquarium Water Parameters)


A stable pH is very important in maintaining a healthy and stress free reef community. As mentioned above, a daily pH shift of +/-0.2 is normal in marine aquaria. Ocean water pH is 8-8.3, and marine aquariums should maintain a pH between 7.8-8.5.

In depth:

“Several factors make monitoring a marine aquarium’s pH level important. One is that aquatic organisms thrive only in a particular pH range, which varies from organism to organism. It is therefore difficult to justify a claim that a particular pH range is “optimal” in an aquarium housing many species. Even natural seawater’s pH (8.0 to 8.3) may be suboptimal for some of its creatures, but it was recognized more than eighty years ago that pH levels different from natural seawater (down to 7.3, for example) are stressful to fish.6 Additional information now exists about optimal pH ranges for many organisms, but the data are woefully inadequate to allow aquarists to optimize pH for most organisms which interest them.7-11

Additionally, pH’s effect on organisms can be direct, or indirect. The toxicity of metals such as copper and nickel to some aquarium organisms, such as mysids and amphipods,12 is known to vary with pH Consequently the acceptable pH range of one aquarium may differ from another aquarium’s, even if they contain the same organisms, but have different concentrations of metals.

Changes in pH nevertheless do substantially impact some fundamental processes taking place in many marine organisms. One of these fundamental processes is calcification, or deposition of calcium carbonate skeletons, which is known to depend on pH, dropping as pH falls.13 …The acceptable pH range for reef aquaria is an opinion rather than a clearly delineated fact, and will certainly vary with the opinion’s provider..”