Saltwater vs. Freshwater

There are literally countless different types of aquariums that you can set up and maintain, there truly is no limit to the variations of size and types of aquatic ecosystems that you can design!  Knowing the differences between saltwater vs. freshwater aquarium systems and fish will help round out your knowledge no matter what type of aquarium you choose.

Introduction

The types of aquariums that are best suited for a home system will however generally fall into one of many categories.  We will review the most common types and separate them into saltwater vs. freshwater categories.  We will also dedicate separate pages to examine the aquatic plants and saltwater corals found in several types of aquariums in more detail.

⇐Aquarium Plants         Aquarium Corals⇒

There are some specialized types of aquariums that we will not go into much detail with as they are not common and definitely not for anyone other than an extremely experienced and dedicated aquarists.  Some examples of these aquariums would be aquariums for large sharks such as nurse sharks, aquariums for octopus, aquaculture farms, fish breeding systems, and cold water aquariums.  Many of the same filtration and animal husbandry principals would apply to those systems but they require significantly more detailed technical knowledge, exacting parameters, and sheer dedication to successfully pull them off.

Although saltwater vs. freshwater aquariums seem worlds apart they are actually not that different and the types of aquariums you can set up with each will have parallels with one another.  You can just go learn the types of freshwater and saltwater aquariums directly but learning the differences between the two types of systems and the differences between the fish available will help you broaden your understanding of aquatic ecosystems.

⇐Types of Freshwater Tanks          Types of Saltwater Tanks⇒

Saltwater vs. Freshwater

saltwater vs. freshwater
Hydrometer used to measure Salinity in Aquariums $6.99

As far as the water goes, the primary difference between a saltwater vs. freshwater aquarium will be … wait for it … salt!   Salt is present in vast quantities in the sea where it is the main mineral constituent, with the open ocean having about 35 grams (1.2 oz) of solids per litre, a salinity of 3.5%.  Salinity is most commonly measured in home aquariums with a simple hydrometer which is a simple tool that measures specific gravity.  Recommended specific gravity for most marine aquariums is between 1.021 and 1.023 and for most reef aquariums is between 1.024 and 1.026.  If you only have fish it’s a little lower because that will allow more oxygen in the aquarium system and fish will do well with slightly lower salinity.

Also pH will be alkaline in a saltwater aquarium.  However, they can be just as alkaline in some freshwater aquariums such as is preferred by many African cichlids and brackish water fish so pH is not necessarily a defining factor.  A saltwater tank will NEVER be neutral or acidic unlike a freshwater aquarium however.  pH is basically a measure of positive and/or negative ions (specifically Hydrogen ions) and their ratio in the water.

saltwater vs. freshwater
Aquaripure Carbonate Buffer $9

A pH of 7.0 is considered “neutral”, a pH above that is considered “alkaline” or “hard” and a pH below 7.0 is considered “acidic” or “soft.”  Rainwater is usually “soft” whereas ocean water and the water in some freshwater lakes is naturally “hard.”  A saltwater aquarium will have a pH between 8.1 – 8.4.  The pH can be raised by using special buffers or even just sodium bicarbonate, ordinary Baking Soda.  Aquaripure Carbonate Buffer is a blend of Calcium Carbonate, Sodium Carbonate, and Sodium Bicarbonate ideal for maintaining the pH in both saltwater aquariums as well as cichlid tanks and other hard freshwater tanks.  The Calcium Carbonate adds just enough calcium and hardness to the water, the Sodium Carbonate increases the pH, and the

API High Range pH Test Kit $12
API High Range pH Test Kit $12

Sodium Bicarbonate primarily buffers the tank which means the pH will be more stable.  We recommend you test pH weekly, when it drops below 8.1 add Carbonate Buffer to the tank to bring it back up over 8.3.  The API High Range pH kit is perfect and more than accurate enough for this task.  When you make a fresh batch of saltwater for an aquarium using commercially available sea salt mix it will naturally be in the correct pH range but it will decrease over time.  In a hard freshwater aquarium you will need to add the buffers necessary to increase the hardness to the correct level and continue to monitor and maintain the hardness level.

Other than the salinity and pH maintaining a saltwater vs. freshwater aquarium is very much similar other than the variety of fish and animals available in each type of system which makes the differences between the two type of systems seem greater than they really are.

Live Rock 20 Pound Salt Water Fish Aquarium $75.00
Live Rock 20 Pound Salt Water Fish Aquarium $75.00

One striking difference is the pink rocks called “Live Rock” found in most saltwater aquariums.  These are calcium based rocks actually made by a species of algae called Coralline algae.  The Coralline algae actually makes the rock and absorbs sunlight for energy just like green plants do.  However, the mechanism by which they do this is slightly different and instead of having green chlorophyll like plants on land and in freshwater systems, they are pink or reddish.  This is also why many of the corals commonly found in marine aquariums have more of a pinkish/reddish color to them.  If whenever you look at a saltwater aquarium you see pink or reddish colors you instead imagine them being green plants then you will understand the purpose of the coloration.  The live rock and corals found in marine systems can seem like alien plants from an alien world when compared to freshwater aquariums.  In fact most corals are technically animals that have these single celled “plants” living inside them in a mutually beneficial relationship!  Bizarre, isn’t it!?!  Even more bizarre is that many corals

Close up of a Saltwater Coral
Close up of a Saltwater Coral with Pink Photosynthesis Molecules

are actually colonies made up of many of these tiny animals!  In addition to absorbing energy from sunlight similar to plants the little animals that make up corals also filter seawater and eat tiny microscopic organisms that are in the ocean!  The animals that make up corals are actually related to other sea animals such as jellyfish, anemones, and even starfish.  They really are alien when compared to the plants and animals that we are more familiar with.  Of course there are some marine plants that use green chlorophyll as well and we will dedicate a special section to those saltwater vs. freshwater plants as well.

Saltwater vs. Freshwater Fish

A Colorful Saltwater Wrasse, research BEFORE buying!
A Colorful Saltwater Wrasse, research BEFORE buying!

The saltwater fish that live in this unusual and alien world of coral reefs are amazingly colorful and varied.  They can without a doubt be more colorful than their freshwater counterparts.  This is part of their appeal and why a saltwater aquarium can be so desirable for an aquarist.  Anyone who is interested in a saltwater aquarium simply must understand this.  A saltwater aquarium will cost several times more to establish than a freshwater aquarium.  The fish can be more rare and endangered.  Many saltwater fish should NOT even be sold and will even not live if you buy it.  Most saltwater fish will not be compatible with each other.  NEVER simply take the word of the guy in the fish store … NEVER.  NEVER make an impulse buy without doing research … NEVER.  NEVER buy a fish based on appearance … NEVER.  A saltwater aquarium will cost several times more to maintain and will take more time to maintain a saltwater vs. freshwater aquariums.  You MUST be FULLY prepared for the financial and time investment a saltwater aquarium requires.  We would also strongly recommend you start off with at least a 10-20 gallon freshwater planted system before you attempt a saltwater aquarium.  If you can successfully manage that then imagine the work and time and money you put into it and multiply that by several times (and then several times again for bigger systems) and you can then decide whether or not the saltwater aquarium will be the right choice for you.

Although saltwater fish can be more colorful than freshwater fish, there are plenty of colorful freshwater fish as will.  Other than general coloration and color patterns, I will review the other main differences between saltwater vs. freshwater fish next.

School of Colorfuk Freshwater Neon Tetras
School of Colorful Freshwater Neon Tetras

There are far, far more varieties of schooling freshwater fish, especially the smaller ones.  As far as saltwater fish goes, the various Chromis species and Cardinalfish species will be the primary species of schooling fish that are available.  There are no small schooling saltwater fish that are comparable to the neon tetra for example and they are all about the size of large Black Skirt Tetras or larger.  Of course, in the ocean there are vast quantities of schooling fish of all kinds, it’s just that most are larger or not available or suitable for a home aquarium and are more suited for lunch such as sardines and anchovies.

A Firefish, happy to be alone.
A Firefish, happy to be alone.

There are a lot more species of small to mid size solitary fish that do well in saltwater vs. freshwater aquariums.  These include Basslets, gobies, blennies, hawkfish, tangs, dartfish, clownfish, and more!  In fact, the majority of saltwater fish available will do quite well as the only fish of their species in a saltwater aquarium provided all their other needs are met and they have fish of other species but similar temperament to keep them company.  There are some freshwater fish like this such as pleco’s, puffers, catfish, bettas, bichirs, and a few others but for the most part freshwater fish are more likely to be better off kept either in schools or small harem groups.

There are some saltwater fish that prefer or can be kept in small harem groups such as anthias and wrasses.  Even a single wrasse male will do fine alone however.  We imagine the differences are due to the larger expanse of the ocean and the great hiding places a rocky coral reef provides and the fundamentally different nature of coral reefs when compared to natural freshwater environments.  Corals will have their own specific requirements for their care and have their own web page on our site.  In contrast freshwater fish come from many different lake and river environments and one of the biggest sources of freshwater fish species is the Amazon basin.

arowana
Large Freshwater Arowana Fish from the Amazon River

With both saltwater and freshwater fish there are several species of large and/or predatory fish to choose from if that’s the type of aquarium you would like to have.

With both freshwater and saltwater fish there will be passive fish, semi aggressive fish that will be passive or aggressive depending on their tank makes, and more aggressive fish that should only be kept with other aggressive fish or fish that will be able to tolerate it and defend themselves.  Review the fish compatibility page for more on that topic.

Understanding the types of fish and some of the fish behaviors common to as well as the differences between saltwater vs. freshwater fish will better help you understand the many different types of freshwater and saltwater aquariums.

⇐Types of Freshwater Tanks          Types of Saltwater Tanks⇒

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