Understanding the standard water parameters for a marine aquarium and how they can change in the aquarium will provide a great step in maintaining a healthy environment for the aquarium inhabitants. Knowledge of what to test for and how to correct conditions when readings are out of their natural range will be essential for success. At times it might seem like a course in basic chemistry, but with a little practice and experience, the strange-sounding terms used will become second nature. The user needs to be able to “talk the talk” to intelligently discuss their marine aquarium.

Since the marine environment means there is a fair amount of dissolved salts, a good understanding of the standard level is required. The most common measure of the level of dissolved solids (salinity) is the specific gravity of the water. Absolutely pure water is given a specific gravity of 1.000. When solids are dissolved in the water, the water becomes heavier per the same volume. Marine environments will have approximately 18 pounds of dissolved salts in 50 gallons of water. This gives a specific gravity reading of 1.022 (S.G.). The actual range of values is usually between 1.021 and 1.024 (S.G.), though some hobbyists keep their marine aquariums as low as 1.018 (S.G.).

The specific gravity is read by using a hydrometer that either floats in the aquarium or has a floating lever in a hand-held device. For most aquarium purposes, these readings are accurate enough, but if really accurate readings are required, the user will have to use either a Salinity/Conductivity meter or a Refractometer. While these may read in specific gravity, they are more likely to read in parts per thousands (35 ppt = 1.026 S.G.) or in MicroSeimens, possibly requiring a conversion table. Since the salinity will rise as water evaporates, it is important to top off the aquarium with pure water and test the salinity frequently to maintain a constant environment. Before a partial water change it is best to mix up any new salt water for a day with aeration to ensure that the salinity level is correct for the aquarium. The user may even have to place a submersible heater in the mixing container to get the water to the proper temperature. With a larger mixing container, it may be best to use a submersible pump and flexible tubing to pump the new water to the aquarium.

During the initial break-in period for the aquarium, it will be important to measure for ammonia and nitrite (please see article on Cycling the Aquarium). Once this period is over, these two readings should be as close to 0.0 PPM as possible. Check these levels once a month, or whenever the fish/corals look stressed. Any time an antibiotic is added to the aquarium, there is a good chance that the biological filtration will be damaged and these two levels may rise temporarily. If so, the fish can be protected by the addition of AmQuel or Ammo Lock and/or partial water changes.

The pH value of the marine aquarium should be between 8.0 and 8.4. This value can change over the course of the daylight cycle because of the action of the algae absorbing CO2, effectively raising the pH level. This small fluctuation is fine, but if levels start to drop below 8.0, it could indicate too high of a fish load and/or not enough water changes. In the mini-reef aquarium it may indicate a depletion of the buffering capacity (carbonate hardness, KH) that would require addition of buffers to help stabilize the pH value. Most test kits for pH will give general readings, but it will difficult to “see” the difference between 8.0 and 8.1. For this reason, many hobbyists use an electronic pH monitor to get a digital reading and to be able to get a constant readout of the pH value just by glancing at the monitor. This monitoring function is also built into many of the more complex mini-reef controller systems that activate the lights, pumps, ozone generators, etc.

As mentioned above, alkalinity (KH or buffering capacity) can play an important role in the mini-reef aquarium’s pH value. While alkalinity and KH are actually separate values, for most aquarium purposes they will be used interchangeably, but make sure you know which the test kit is reading, the values are different. Alkalinity is usually expressed in millequivalents/liter while KH is described in parts per million (PPM). Yet another term associated with KH will be German degrees of hardness, dKH. Different test kits will express their results in different units, so it is important to know how to convert from one to the other. The following chart gives most conversions:

1 meq/l ………………………… 50 PPM (CaCO3)

1 dKH …………………………. 17.9 PPM (CaCO3)

## PPM……..times 0.05……….. ## dKH

## meq/l …….times 2.8……….. ## dKH

In the mini-reef aquarium, as the corals, coralline algae and anemones grow, calcium will be removed from the water. Calcium also plays a part in the buffering system as Calcium Carbonate (CaCO3). If the calcium levels get too low, this can cause depletion of the buffering capacity, causing the pH to drop. This will also inhibit the growth of the corals. Additions of calcium supplements, partial water changes and buffers can help prevent this. The natural seawater alkalinity is between 2.1 and 2.5 meq/l (100 to 150 PPM). Many reef hobbyists raise this to 5 to 6 meq/l and have reported success. Any time the pH level seems to be off, or (weekly) when adding calcium supplements, it will be a good idea to measure either alkalinity or carbonate hardness. Natural seawater has a KH value of 7 dKH, while mini-reef aquariums are often kept close to 12 dKH.

There has been some recent controversy as to the proper temperature to keep the mini-reef aquarium. Most texts will state that it should be kept between 74 and 78 F. With the large lighting systems and water pumps required, this is sometimes difficult to do, and may even require the use of a chiller unit to keep the temperature in range. A few recent studies have suggested that the temperature can be as high as 84 to 85 F without harm, though others “see” problems at any temperature above 82 F. Until this issue is addressed by more hobbyists, it is probably best to keep the temperature in the mid 70’s. In a “fish-only” style marine tank, as long as there is sufficient water movement and aeration, the temperature could climb to the mid 80’s before the fish would be overly stressed.

Testing for
should be done weekly. This number is the best indicator to determine if enough water is being changed. In a fish-only aquarium, the number can be over 100 PPM without obvious effects, but ideally should be kept below 40 PPM. In the mini-reef aquarium, it is best to try to keep this number below 10 PPM, as nitrate is one of the primary sources of nuisance algae growth. If levels exceed these limits, then either more water changes are required, or use of one of the denitrification reactor might help. Cutting back on the fish load and feeding will also help slow down the build up of more nitrate. The addition of an efficient protein skimmer can also slow down the build up of excess nitrate by removing organic wastes before bacteria can digest them to nitrate.

It is possible to test for the oxygen and carbon dioxide levels, but most of the time this is not necessary. Normal oxygen levels would be 6 to 8 PPM, while CO2 would be between 45-55 ml/l. With normal water movement, it would be rare for either of these levels to be too high or too low.

Copper is one metal that can be in the tap water or be used to treat parasites (in a NON-mini-reef tank). Ideally there should be almost no copper in the aquarium. When treating with a copper agent, the levels should be between 0.15 and 0.25 PPM for an effective dose. Once the treatment is finished, the copper should be removed with some kind of treatment, i.e. Polyfilters, Cuprisorb, etc. Copper is deadly to invertebrates, so should never be present in a mini-reef aquarium. Be aware that some treatments use a chelated copper to make the dosing simpler, but if used in the presence of ozone or UV treatments, the chelated bond could be broken, releasing excessive amounts of copper into the tank. Care should always be taken with copper treatments as some are labor intensive. As with all types of treatments, it is best to use a quarantine/hospital tank for the treatment period.

Phosphate levels are nice to know since this is also one of the primary food sources for alga. The lower this level is kept, the better. In the home aquarium it is considered a victory if the level is below 0.1 PPM, though natural levels are 0.0003 PPM! There are several phosphate-removing agents, i.e., PhosGuard, Phos Zorb, PhosBan or Phosphate Removing Pads that can be utilized to help keep the phosphate levels down. The use of a refugium style filter can also help lower phosphate (and nitrate) levels in the marine aquarium. Sometimes the hobbyist will have to also use a reverse osmosis unit or deionizing resin to remove phosphate from the tap water. Many cities are now adding significant amounts of phosphate into the tap water to prevent lead leaching from older plumbing pipes. For most marine applications, you would want to use a combination Reverse Osmosis and De-Ionizing system (RO/DI).

Mentioned earlier was the importance in monitoring the calcium levels to prevent loss of the carbonate hardness and a drop in the pH. Natural levels are 350 to 400 PPM, and in the home mini-reef, levels from 300 to 500 PPM are not unusual. This will help maximize the growth of the corals and coralline algae, and that in turn helps prevent the growth of nuisance alga. Most calcium test kits are a titration test kit. This means that chemicals are added to the testing chamber, then another agent is slowly added, drop by drop or with a small syringe. The number of drops (or milliliters) will then be compared to a conversion table to see what the actual calcium level is. A thriving mini-reef will require the addition of a calcium supplement daily to keep up with the demand from the coral and coralline algae. Often this can be mixed with the water added to top off the evaporation loss. There are numerous types and styles of calcium additives on the market, it is best to get one that will be used correctly.

While at first this may seem to be a daunting amount of information and testing just to have an aquarium, after a few weeks of practice, it will become part of the routine and require little thought. This is a case where a little bit of preparation and practice can go a long way to the success of the aquarium venture.

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