Saltwater Aquarium Chemistry & Water Quality

Saltwater Aquarium Chemistry & Water QualityRed Sea Test Kit

The foundation to keeping a thriving and healthy aquarium begins with keeping your water quality in check. When you do regular water tests and keep parameters in check, your fish and corals will be more colorful, grow bigger and be more disease resistant. In a previous article, we outlined general recommendations for each aquarium parameter. In this article, you will gain a basic understanding of how these parameters effect your aquarium inhabitants and how they can be changed and improved. This information is a basic introduction and a more comprehensive analysis of aquarium chemistry can be found on by a long-time reef chemist and thought leader in the aquarium industry; Randy Holmes-Farley (



** Please Note: These suggestions are basic introductory guidelines for reef aquariums. Some species of fish, coral or invertebrates may require different water parameters. We recommend consulting with a trusted source before purchasing and introducing any livestock into an aquarium.


Suggested range is 1250-1350 ppm

Magnesium should be added before adding Calcium and Alkalinity in your aquarium. Magnesium acts as a “barrier” between Calcium and Alkalinity molecules so they don’t create a chemical reaction in your aquarium and precipitate. If calcium and alkalinity are precipitating in your aquarium, you may see a white powdery substance on your heaters and pumps. If calcium and / or alkalinity are added too quickly, your water may even have a milky appearance (it will look like a snow storm in your tank). Magnesium is consumed by corals far less than calcium and alkalinity, and is generally dosed after a water change. Do not raise magnesium by more than 100ppm per day; and if necessary, spread the doses out over multiple days. Always test your levels first and then dose very slowly to a high flow area.


Suggested range is 380-450 ppm

Calcium is readily consumed by beneficial Coralline Algae and hard/stony corals to help them grow their skeletal structure. To increase calcium levels, the easiest (and best) way is to use a quality aquarium salt when doing your regular water changes. You can also use Kalkwasser in your top off water, dose a liquid calcium additive or use a calcium reactor (use as directed). Do not raise magnesium by more than 50ppm per day; and if necessary, spread the dose out over multiple days.


Suggested range is 125-200 ppm or 7-11 dKH or 2.5-4 meq/L

Like calcium, corals also use alkalinity to build their skeletal structures. Alkalinity can have an effect on pH, but should not to be confused or interchanged with pH. Some alkalinity additives like Soda Ash (Sodium Carbonate) will increase the alkalinity and pH of an aquarium. Other additives like Sodium Bicarbonate will increase alkalinity, but have little or no effect on pH. To increase alkalinity levels, you can use Kalkwasser (Lime Water) in your top off water, use a alkalinity additive, use a high quality reef salt or use a calcium reactor (use as directed). Monitor pH when initially adding an alkalinity supplement so the pH doesn’t increase by more than 0.20. Do not raise alkalinity by more than 0.5meq/L or 1.4 dKH per day; and if necessary, spread the dose out over multiple days.


Suggested range is 7.8-8.5 pH (a range of 8.1-8.3 pH is better)neptune-apex-standard-ph-probe

A common misconception with pH is that it always needs to be maintained at about 8.4, however, if your aquarium is constantly at lower numbers within the suggested range, there isn’t anything to worry about. In addition, an aquarium will generally have a higher pH during the daytime because algae will consume Carbon Dioxide (CO2) expelled by animals in the aquarium (CO2 is acidic). During the night when photosynthesis stops, CO2 levels will increase and pH will start to drop (this is perfectly normal). Due to gas exchange with the surrounding environment, pH can also drop quickly if there are a lot of people in your home (opening a window for fresh air can help mitigate this). If you use Kalkwasser (Lime Water) or Soda Ash (Sodium Carbonate) in your aquarium, it is extremely important that your pH doesn’t rise too quickly or above 8.5. Conversely, a calcium reactor can cause your pH to drop dangerously low without proper controllers and redundancy. An advanced method of measuring pH is with an aquarium controller that has a pH probe.


Suggested number is 0 ppm

Ammonia is toxic to all fish and corals and should be undetectable (0 ppm) on a test kit. An elevated amount of ammonia can mean too many animals were added to your aquarium in a short amount of time, something died, or the aquarium is cycling. If you have a new aquarium, it can take 2-10 weeks (or more) for the “cycling” process to complete. As beneficial bacteria populate the aquarium, the bacteria will consume ammonia and convert it into nitrite. Here are a few options to help reduce ammonia.

Instant Ocean Bio Spira1) For established tanks, inspect for any dead fish.

2.) For new tanks, an artificial bacteria supplement can be used like Instant Ocean Bio Spira.

3.) For new or established tanks, clean or pre-cycle new rock additions before putting them into the display (dry and dead material on rocks will decompose and release ammonia, nitrite and phosphate into the aquarium).

4.) Don’t over feed your tank as uneaten food (and fish waste) will decompose to create Ammonia.

5.) Don’t add too many fish in a short amount of time. An increased amount of fish will also increase the amount of fish food and waste (which breaks down into ammonia). Add fish to your aquarium slowly so that beneficial bacteria in your tank can safely multiply and eat the waste from your new fish.


Suggested number is 0 ppm

Like Ammonia, Nitrite is also toxic to fish and corals and should be undetectable (0 ppm) at all times. In the cycling process, ammonia is consumed by bacteria and converted to Nitrite.


Suggested range is less than 1 ppm

Nitrate less than 20 ppm are mostly harmless to your fish and corals, but can fuel algae growth and give your corals a dull or brown appearance. In the aquarium, nitrate is a byproduct of the cycling process (Ammonia converts to Nitrite, then converts to Nitrate). Possible solutions include:

ati_powercone_2001.) Remove bio balls from your system as this will trap fish waste and uneaten fish food (bio ball filters are best for fish-only tanks).EcoTech-Marine-VorTech-MP10wES-Propeller-Pump-w-Wireless-EcoSMART-Driver-99

2.) Don’t over feed your fish and corals as uneaten food (and fish waste) will decompose and create nitrates,

3.) Improve water flow in your display tank to keep fish food and fish waste from settling on the sand bed (this allows the skimmer and filter sock to readily remove these from the system).

4.) Make sure your skimmer and other filtration are clean and sufficiently removing waste and debris from the tank

5.) Use bio pellets. Bio pellets grow beneficial bacteria on the surface of the pellet that consume nitrate. Use bio pellets only as directed.


Suggested range is less than 0.03 ppm

Since these low levels can be difficult to measure, an acceptable range is less than 0.10 ppm. Phosphate is the fuel that grows algae and is naturally found in fish food as a preservative. Over feeding and over stocking your aquarium can be a leading factor to high phosphates. It’s also suggested to ensure your filtration is clean and sufficiently removing waste and debris from the system. A phosphate removing media like GFO (granular ferric oxide) can help adsorb phosphate from the aquarium, but requires a media reactor and regular maintenance.

Water Temperature:

Suggested range is 74-82 degrees FahrenheitEheim-Jager-TruTemp-50-Watt-Fully-Submersible-UL-Approved-Heater-99

A water temperature outside this range can create elevated levels of stress on fish and corals. If your aquarium is too cold, make sure your heater is the proper size and working (we always recommend keeping a backup). If your aquarium is too warm, a simple fan can be used to move air across the top of the water and opening up the stand to allow air movement inside the sump (evaporative cooling). If there is an emergency, turn off the lights and put zip-lock bags of ice in the tank. During hot summer months, keep a couple pop bottle filled with filtered water in the freezer as a backup. If temperature is problematic, consider eliminating metal halide lights, switching to an external water pump or using an aquarium chiller. Always use an easy to read thermometer and check it when you’re feeding your fish.


Suggested daily light cycle s is 8-10 hours

Lighting greatly depends on the animals within the aquarium, but generally should not exceed 10 hours for reef aquariums. The intensity of every light is different and in the case of LED or Metal Halide lights, many people will start them at about 50% intensity or raise them higher off the water so their corals don’t get too much light and die. Too much light can also encourage nuisance algae growth. We recommend changing out light bulbs every 10-12 months (except LED lights – which can last several years).

* LED – new technology to the reef hobby with many options (dimming, colors, etc.). LED lights cost more up front, but save money over time because they’re more efficient (lower electric bill) and have low running costs (no more changing light bulbs).AquaticLife-24-Inch-2x24-Watt-T5-HO-Light-Link-Fixture-Marine-98

* Metal Halide – great for corals requiring a lot of light. These lights can get very hot and raise the tank temperature. The up-front cost is less to purchase Metal Halide lights, but your electric bill will be higher, and the bulbs are expensive to replace.

* T5 High Output – a great, low-cost and economical option for people who love corals. There are a small number of corals T5 lights may not be able to support (like some types of “Acropora”).

* Power Compact (PC) – an older style of light that can grow low-light soft corals.

* T8 Fluorescent – only recommended for fish only aquariums.