Saltwater Guide

Many people consider setting up a marine aquarium but are nervous because they have been told that saltwater is “difficult to maintain.” This hand out is designed to give you an idea of just what is “difficult” about saltwater, what isn’t, and how you can prevent costly mistakes, ultimately leaving you with enough essential information to decide if a marine aquarium is for you.

If you decide to “dive in” to a saltwater aquarium, this guide is only a starting point. We will recommend several books (and a couple of other hand outs) along the way that will help you in your quest for good information and ethical aquarium keeping. As always, ask questions.

The most common question asked is: What’s the difference between saltwater and freshwater? The most basic answer is that there is salt in the water and that the new saltwater for water changes should be mixed 24 hours in advance of the change. Salinity (the level of salt in the water, usually measured by a hydrometer as specific gravity) must be monitored and kept constant. If water evaporates, the salinity changes, so evaporation must be controlled and compensated for by adding freshwater.

But the comprehensive answer goes beyond salt. Stress is the main factor in fish illness, and stress comes from a variety of sources. Marine fish (and invertebrates), for the most part, are wild caught animals and are not accustomed to life with glass walls for boundaries. Limiting their territory, and their ability to move on to find food and new territory, is a somewhat stressful experience for a previously “free” fish, especially for the first few months.

With fish, as with people, conflict between individuals is stressful. If two fish that do not get along are kept in close quarters one or both will eventually become stressed from the battles that ensue. If two people do not get along one can leave the room, but fish are confined to the aquarium in which they are kept. Most saltwater fish get large and need ample opportunity to establish territory.

Water in the ocean (which these fish are accustomed to) contains high levels of dissolved oxygen. Lack of air creates more stress, again creating a greater chance for fish illness; therefore, high levels of dissolved oxygen in a saltwater aquarium are essential. For these reasons, the fish population in marine aquariums is kept much lower than in freshwater. Usually one fish per ten gallons, sometimes even less, is the basic rule in saltwater. A less dense population also makes the spread of parasites to all of the fish in the tank less likely, thus giving another good reason to keep the tank lightly stocked.

Also to prevent the spread of parasites, a saltwater aquarium should be stocked more slowly than freshwater. The life cycle of the “ich” parasite in saltwater can be as long as a month. So ideally, a new fish should be added to the aquarium no more than once per month. (For more information on treating ich see our hand out “Preventing and Treating Saltwater Parasites.”).

Another question people usually have about saltwater aquariums is: What equipment do I need?

The same power filters or canister filters used in freshwater can be used in a saltwater setup. The same heaters may be used as well. The key here is to select dependable supplies. Since the fish are more expensive and more sensitive, it is worth your while to upgrade to a filter or heater that is of better quality and more reliable. They will keep the temperature more stable and the water circulating dependably and in the end might save a lot of money and grief. We recommend a back up in addition to your main filtration system in all tanks, such as a sponge filter, a power head, or even just a big air stone. We do not, however, recommend under gravel filters for either saltwater or freshwater. (For more details, see our hand out “Under Gravel Filter Controversy.”)

Depending on the type of set-up chosen, additional necessary equipment may include an ultra-violet sterilizer, a protein skimmer and/or some additional power heads. More detailed use of these items will be described later.

Crushed coral is used as substrate in most saltwater aquariums. It helps to maintain the high pH that is enjoyed by marine fish. A hydrometer is used to measure the specific gravity of the water in the tank and for water changes; a good salt mix, which raises the pH to the proper level (8.2-8.4), should be used to make the water. We carry two grades of salt, one used for fish only aquariums and one that contains extra trace elements essential for keeping invertebrates.

More initial questions to answer include: Are saltwater fish hard to keep? What about invertebrates? Which fish get along?

Since there is a variety of hardiness levels and dietary needs amongst marine animals, some are harder to keep than others. However, in general, keeping a marine animal happy requires three basic things:

  • Diet: Different fish have different dietary needs. Feeding a fish, or invertebrate, the foods that approximate what it would eat in the wild is a good place to start. Giving a fish the variety that is available in nature will help to round this out. There are many frozen, flake, and dried foods to help meet the nutritional needs of several different families of marine fish and invertebrates, as well as HUFA (Highly Unsaturated Fatty Acids) vitamins to add to frozen foods to help replenish nutrients lost in the freezing process. Don’t expect any marine fish to eat the same thing for every meal, every day. In the marine hobby, there are a lot of species, both fish and invertebrate, which may be offered, that do not typically survive in captivity for a number of different reasons. Some don’t eat, some aren’t practical to feed. Others may eat, but despite best efforts, waste away because it is impossible or impractical to provide the specific foods they need in captivity. Some aren’t entirely understood making it even more difficult to provide for their needs. Knowing the requirements for keeping a fish or invertebrate will make it easier to keep, or avoid (if you are unable or unwilling to provide for its needs).
  • Water quality: Water quality is always important in any aquarium, but especially in saltwater, and even more specifically for certain fish and almost all invertebrates. Water changing frequently and not over-feeding, along with the use of a protein skimmer and perhaps some chemical absorption products, are key in keeping water quality acceptable and animals healthy.
  • Replicating the natural environment: Reef dwelling animals prefer reef-like environments. Open water fish like open environments. Some fish or crustaceans need a special little hole or cave for sleeping or relaxing. Whatever the habitat of the particular creature is in the wild must be provided in the aquarium. A dwarf angel or butterfly fish will not thrive in a tank where there are a few scattered fake corals and no rock structure for them to swim through. The more comfortable a fish is in its environment, the more often it will be seen and the healthier it will be.

Regardless of natural habitat or dietary needs, a tank-raised, captive-bred, or farm-raised fish will always be hardier than its wild-caught counterpart. A number of clownfish, dottybacks, gobies, seahorses and some other organisms that are not wild-caught are available.

When selecting fish for the aquarium there are some basic guidelines that make them more likely to cohabitate agreeably and remain happy, healthy, and well fed. (Keep in mind that fish do not read books and sometimes do not follow the “rules” that have been established for them. Certain individuals of a species may not act like the majority of them do.):

If a fish will fit into another fish’s mouth it will probably end up there, so select fish accordingly.

The more fish look alike and the more closely related they are the less likely they are to get along. An angel will tend to be more aggressive toward another angel, and a blue fish will be more likely to harass another blue fish, especially if they have a similar body shape.

Aggressive eaters should not be kept with timid eaters. Fish that are assertive and have sharp teeth, like triggers, should not be kept with long-finned or small fish like lionfish, batfish, or blennies. Some puffers and triggers are extremely voracious eaters and will keep almost all other fish from sharing in the food.

We recommend reading a variety of books to find out about the specific fish and invertebrates of interest. We recommend the following books: Marine Fishes by Scott W. Michael (for fish), Invertebrates: A Quick Reference Guide by Julian Sprung (for all invertebrates) and Aquarium Corals: Selection, Husbandry, and Natural History by Eric H. Borneman (for corals and other related animals). These books give feeding requirements, general hardiness levels, tank size requirements, other special provisions, and typical personality and aggressiveness levels of different groups of animals commonly available in the aquarium trade. These books are good in helping to select which of the marine animals are practical to keep in your particular set-up. They help you to take into consideration your current experience level and the amount of extra effort you wish to put into your aquarium.

The Most Common Saltwater Mistakes

The information given here is based on years of experience and information gathering. Sometimes the rules can be bent successfully, but more often than not the results of this will be disappointing.

  1. Adding fish without respect to the tanks’ age: Adding fish during the break-in cycle, not using hardy fish for the break-in cycle, and adding fish that need a well aged tank too early, will almost always lead to disappointment.
  2. Adding new fish too close in succession: To minimize parasite problems and stress there should be at least two weeks between adding fish, preferably one month, and they should be added one at a time.
  3. Not quarantining new fish: All new fish added to an aquarium should be quarantined for two weeks, ideally in copper. All fish at Aquatics Unlimited have arrival dates on their labels, and it is preferred that they remain at the store for two weeks from that date. Our two week “layaway” makes this easy for our customers. Having a quarantine/hospital tank at home also makes it easier to treat fish illness down the line without treating the entire show tank.
  4. Over feeding/ not water changing often enough: These things lead to high levels of organics in the tank (measured as nitrates) which stress out both fish and invertebrates, making them more prone to illness and can even cause death.
  5. Over crowding: Stocking the tank with too many or fish that get too large leads to high waste levels, more likelihood of parasite infestations, and more territorial battles.
  6. Not feeding properly: Not feeding fish that need specific elements in their diet the particular elements that they need, not giving good variety, and feeding only flake food to most saltwater fish may lead to lateral line erosion, constipation, and death.

Choosing the type of marine aquarium

There are five different basic types of marine aquariums. Some animals only work in one or two types of aquariums; others will work in almost any. It is recommended that a “wish list” be designed to establish what fish are desired for your aquarium. This makes it easy to check for compatibility, what the needs are, and the order in which they might be added with respect to the level of territoriality and how old the tank should be before they are added. This process helps to prevent disappointment down the line.

The fish only aquarium would generally have crushed coral for substrate, hiding places made out of rocks, artificial plants, and dead or artificial coral heads. (We recommend use of the artificial corals, as they do not contribute to the destruction of the coral reefs.) This tank would commonly be kept coppered (to prevent parasites) until fully stocked. A fish only aquarium may also contain live rock, as some reef dwelling fish get a significant amount of their food by grazing on live rock. It is then recommended to use an ultra violet sterilizer to help prevent parasites, as most effective parasite treatments (such as copper) will destroy the life on the live rock. (An ultra violet sterilizer is a small housing containing a light bulb that produces ultra violet light. The sterilizer gets attached to a canister filter or power head, and as the water flows through it almost everything in it will be killed. This is effective in killing most of the baby parasites that live in the water before they attack the fish.)

Salinity, measured as specific gravity, can be kept low in a fish only aquarium. Typical specific gravity for the water in such a tank would be 1.018-1.021. Lower specific gravity helps to prevent parasites. Nitrates should be kept at 80 ppm or lower; 30% water changes may need to be done as often as once per week to maintain such a nitrate level. (See our hand out “The Water Change” for details on how to do a thorough and effective water change.)

The temperature in such a tank would generally fall within the 74-78°F range. Whatever temperature you choose, consistency is the key. Fluctuations in temperature (as well as salinity) may lead to parasitic and bacterial infections.

In this case, the bigger the tank is, the better off it will be. Most marine fish get large, and unless you make a point to keep fish that stay small, a large tank (minimum 55 gal) is necessary. A good rule for keeping marine fish is also to have one fish per ten gallons of water. (Be sure that the fish that you chose don’t outgrow your tank size.) This rule is a basic guideline and may be modified for fish that stay very small, those that get very large, or fish that are very mean. This allows room for growth and to establish territory.

Every fish has different dietary needs, but the key is always variety. Much variety is offered in the many different types of frozen foods, and such foods retain more vitamins than many dried foods. Frozen foods offer items that are not otherwise available, and are more palatable for some fish than many flake foods. Some fish will never eat anything other than frozen foods. Flake foods help to “round out” the diet, and offer a convenient, high protein source of nutrition.

It is recommended to feed frozen food to a marine “fish only” aquarium at least one per day, flake food once or twice per day, and dried algae (when appropriate) once a day. Most saltwater fish are grazing fish, picking a little bit of food here and there all day long, so small, frequent feedings are ideal. Flake food or dried flake-type algae should be consumed within 30 seconds, frozen food in 1 minute, and sheet algae can remain in the tank (attached to a veggie clip) to be consumed over the course of a half hour to an hour. It is also recommended that HUFA vitamins be added to frozen food as it thaws. Descriptions of the dietary needs of four popular groups of fish follow.

  • Angels: frozen sea sponge and algae foods, as well as dried algae and algae flake food
  • Dwarf Angels: frozen, dried, and flake algae foods, frozen mysis shrimp, and other chopped meaty frozen foods (also like live rock or well aged aquarium rock to pick algae and organisms from)
  • Tangs and Rabbitfish: frozen, dried and flake algae foods
  • Eels, Triggers, Lionfish, Puffers, and Groupers (carnivores): Some are fish eaters, some are crustacean eaters, and some eat anything that moves. A variety of frozen meaty foods is preferable, but a stubborn carnivore may require live feeder fish, ghost shrimp, fiddler crabs, or crayfish to initiate feeding until they become accustomed to frozen foods. Despite the fact that these fish are carnivores, they should have some algae matter in their diet, such as flake food fed to a live feeder, or the small amount of algae matter included in some frozen meaty preparations. Carnivores that are fed only meaty foods (such as krill or feeder fish) seem to be more likely to stop eating from time to time, and some never start eating again. When fed exclusively freshwater feeder fish long term, saltwater carnivores seem to experience similar impaction or constipation problems whether the feeders are fed flake food or not. Therefore it is preferable to train marine carnivores to eat frozen preparations designed for them.

These are guidelines for these fish as a group. Individual species may have different requirements, and many fish are not listed here. To find specific dietary requirements (along with other useful specs) for specific fish please consult Marine Fishes and inquire before purchasing.

The invertebrate only aquarium is probably the most practical saltwater set-up for a small tank (20 gallons or less), and can often be done without any special lighting. It would typically contain starfish, urchins, shrimps, lobsters, crabs, cucumbers and tube worms. It would be set up similar to a fish only aquarium, but would almost certainly contain live rock, as it should never have to be treated for parasites and many creatures in the tank will feed off of it. Substrate is not required, but would be recommended as some invertebrates like to burrow and dig. A protein skimmer could be helpful in this aquarium, but may not be necessary if the tank is not heavily stocked or overfed. A specific gravity of 1.023-1.025, a temperature of 74-78° F, and a nitrate level of less than 40ppm is essential. Water changes of 30% may have to be done every 2-3 weeks to maintain such a nitrate level, and trace elements such as iodine and calcium may have to be added intermittently. If anemones are to be kept one watt per gallon of lighting, including some actinic (blue) light, is a must, and nitrate should be kept as low as possible. Certain anemones may need more light; others do not need any.

Many crustaceans will gladly graze on live rock, but a tank heavily stocked with invertebrates should be fed a variety of frozen and flake foods every couple of days, in very small quantities (what can be eaten in 30-60 seconds). Tanks containing some of the more carnivorous inverts should be given chunks of frozen meaty foods, such as squid, clams (or other frozen foods that are made up of a combination of such items) three to four times per week. A tank containing urchins or other herbivores that doesn’t have a lot of algae should be fed dried algae at the same frequency. Filter feeders, such as scallops and feather dusters should be fed a liquid food, such as DT’s Phytoplankton, or Marine Snow every 1-2 days.

Species for the fish and invertebrate aquarium must be chosen carefully. Many fish eat invertebrates, and those fish prone to ich will be more likely to catch it with higher salinity and invertebrates present (many invertebrates are believed to carry ich) in a tank where it is difficult to treat it effectively. As fish produce and tolerate significantly more waste than most invertebrates, the fish load should be kept much lighter than in a fish only tank, about one fish per twenty gallons.

Both a protein skimmer, to keep nitrate levels low enough for invertebrates, and an ultra violet sterilizer, to help prevent ich infestations, are recommended in this type of set-up. Feeding should be as recommended for both fish and invertebrates in the previous sections, and tank parameters should be as recommended for an invertebrate only aquarium. Water changes of 30% may have to be performed weekly to keep nitrate levels acceptable. This will help replenish levels of trace elements as well. Some elements (such as iodine) may also have to be added if there is a large number of one type of creatures (such as shrimp or mushrooms.)

The reef aquarium usually doesn’t have substrate, but sometimes has a deep sand bed. A great deal of research should be put into making this decision as to the appearance desired and creatures to be kept with the corals.

In this type of set-up the tank is typically filled with live rock. Sometimes more affordable Paradise Coral Rock sold dry or wet (with bacteria cultures already present) is used as a base, and then nice live rock is added as cap rock. The coralline algae and organisms that come on live rock will spread to the other rock if the tank is well kept and properly lit.

A protein skimmer is a great tool to help keeping levels of organic waste at a minimum. (There is also some chemical absorption products that can be used to help maintain low levels of nitrate, phosphate, and other harmful elements in a reef tank.) An ultra violet sterilizer is highly recommended to prevent parasite problems in a reef aquarium that contains fish. (It can also help to keep undesirable algae under control.) Lighting is essential in reef aquariums. A tank in which hard corals are to be kept should have 3 watts of light per gallon. (A 100 gallon tank would have 300 watts of light.) A tank where only soft corals, mushrooms, and other similar polyps are to be kept should have 2 watts of light per gallon. (A 100 gallon tank would have 200 watts of light.) Either way, some of the light should be actinic (blue) to approximate the light that filters through the water in a natural reef. With such intense lighting, a chiller, rather than a heater, is sometimes necessary to keep the temperature within the desired range of 75-80° F, as most corals do not tolerate temperatures in the middle and upper 80’s.

Power heads, for supplemental circulation, are also commonly added to such a set up, as some corals prefer more water movement and they can be used to direct current in their direction. Tank size for such a set-up is flexible, however most reef tanks are at least 55 gallons to be capable of holding corals and polyps as they grow and spread.

The ultimate goal of this aquarium is to keep corals and decorative clams. The fish and other invertebrates kept in this type of set-up are usually functional; their purpose is largely to eat the different types of algae and detritus, therefore not much supplemental feeding for these creatures is necessary unless a lot of excess decorative creatures are added. Some corals and clams, however, are filter feeders, and need to be fed a liquid food (such as DT’s Phytoplankton or Marine Snow) designed for them.

Although they might be a tempting addition, anemones, as a general rule, should not be kept with corals. An anemone can detach itself from its position at any time and relocate on or near a coral and sting them, causing damage to the coral, even killing it.

To get rid of organic matter, and replenish trace elements, water changes of 10-25% should be performed every 1-2 weeks. Supplements to replenish elements beyond what the water change supplies may also be necessary. There is a multitude of ways to set up a reef tank. These are basic guidelines and it is suggested that a great deal of individual research be done to select what is preferable.

The specialty aquarium is a broad category of saltwater set-ups that could be done in many different sizes of aquariums depending on the animals desired.

  • Seahorses should generally not be kept with other fish, as they are slow, timid eaters that will have their food stolen by most other fish. They can, however, be kept with some invertebrates; a serpent star or a couple of cleaner shrimps make a great scavenger in such an aquarium. Seahorses can be kept in small tanks, but are the one fish that prefers a tall tank. Since seahorses like to swim vertically, a 20High aquarium, or other tall tank, make a perfect home. We recommend farm-raised seahorses for ethical reasons, as the population of seahorses around the world is diminishing. Farm raised seahorses are also much healthier and easier to feed than their wild-caught counterparts. For more information see our handout “Farm Raised Seahorses.”
  • Mantis shrimp, or other fish eating invertebrates, also make interesting displays when kept alone in an aquarium. Since tank mates are usually out of the question, and most species stay relatively small and do not mind a small territory, a smaller tank is a realistic option.
  • Fish with special requirements, such as those that are shy or delicate, or those that will eat almost any tank mates, may also make a fascinating display on their own, but must be kept almost exclusively. Extra timid fish, such as a Pinnatus Batfish, most Anthias, Frog fish, walking batfish, and some deep water fish may be kept alone or with other timid species that will not dominate food consumption. Keep in mind, though, that many of these fish are also difficult to feed and special dedication must be made to keeping such animals. Deep-water species generally need cool water and may need a chiller instead of a heater, and also do not like bright lighting, so traditional tank lighting is out of the question. Some fascinating fish, like scorpion fish and toad fish, will eat almost anything, including fish up to their own size, and need to have tank mates chosen carefully, but may be best kept on their own as well.
  • Though octopus are intriguing and intelligent creatures, they very shy and therefore stress easily. Such an animal should, for ethical reasons, have a rather large aquarium (with dim or red lighting) even for a small specimen. Special care must be taken that all aquarium openings are meticulously covered and that aquarium covers are attached tightly and cannot be pushed off, or the animal will escape. The majority of the time, even if all the proper precautions are taken, an octopus does not last more than a few months in captivity. Often, the excited aquarist brings home an octopus never to see more than a tentacle or two of this shy creature’s body the entire time it is there.
  • Sharks and Rays are fascinating creatures, and some are available in the aquarium trade. However, most species get very large, too large for all but the largest aquariums. Even the smallest, most inactive species require at least a 180-gallon tank. Before even considering purchasing one of these animals, it is recommended to read Sharks and Rays: An Essential Guide to their Selection, Keeping, and Natural History, by Scott W. Michael. This book gives a pragmatic look at the ethical and practical realities of keeping such an animal, what is required for their care, and what species can be reasonably kept in captivity.

No matter what type of marine aquarium is on the horizon, please research it well. Many books offer excellent practical advice and ethical guidance in making purchases for the marine aquarium. For the beginner marine aquarist The New Marine Aquarium, by Michael S. Paletta, is an excellent introduction to the available equipment and methods of marine aquarium care. For the budding reef hobbyist Natural Reef Aquariums: Simplified Approaches to Creating Saltwater Microcosms, by John H. Tullock gives a detailed and expansive look at setting up such an aquarium.