A guide for new marine aquarium hobbyists to help them stock their fish only (FOWLR) aquarium for long term success.


  Beginners guide to fish stocking for a FOWLR aquarium
This guide is intended to help out hobbyists who are new to keeping saltwater fish or new to the aquarium hobby in general and would like to start off with a saltwater aquarium. The livestock stocking advice given is intended to be somewhat generic in nature in that it is based on basic filtration, water flow and beginning marine aquarium experience. While advanced filtration, protein skimming, live rock, water changes, sumps with live plants or algae scrubbers will greatly enhance the number of fish on can keep and the speed at which they are added to the aquarium, this guide assumes basic filtration in the form of a simple wet/dry filter or canister filter. We will touch on all the major factors that are involved with properly stocking a saltwater fish-only or FOWLR aquarium and all recommendations will error on the side of caution. The goal of this beginners guide is to give the beginning marine aquarium hobbyist a solid footing with which to make good decisions on how many and which fish they should keep in their new marine aquarium.

When stocking a saltwater fish-only aquarium, there are four main areas to consider before you invest in your first fish. These four very important aspects of stocking a marine aquarium are dissolved water chemistry, filtration system capabilities, fish compatibility and fish size & swimming habits, all of which are factors in selecting fish livestock. The following discussion breaks down each of these areas to provide the beginning marine aquarium hobbyist with the basic information they will need to quickly be on your way to successfully stocking your marine fish aquarium.
  Water Chemistry
Water chemistry is a good place to start when deciding which type of live stock to keep within a marine fish-only tank. While many fish sold within the marine aquarium hobby are tropical reef fish who require warm water 78 ° to 82 ° with a lot of water movement and high levels of dissolved oxygen, others require colder water temperatures and only moderate water flow. Different fish also have widely different tolerances for dissolved nutrients in the water like nitrate, while Clownfish, Damselfish and other can tolerate higher nitrate levels, other fish like Butterflyfish and Anthias are much more sensitive to higher nitrate levels. Ultimately, the hobbyist will need to choose between a warmer tropical water aquarium or a cold water aquarium.
After deciding on water temperature, comes decisions on how much internal water flow the aquarium will have and how much of the filtration will be dedicated to nutrient export. Hardy fish species can be kept in aquariums with moderate water flow from the filtration return pump and a basic powerhead, while most reef fish or fish considered moderate in difficulty to keep will require strong waterflow that only multiple powerheads will be able to provide. Always provide water flow that is laminar or varied, either through the use of a controller or through strategic placement of powerheads. In larger aquariums powerheads can be placed near the surface and directed to push water towards each other, which will ultimately produce laminar or varied water flow; however, most hobbyists will want use a powerhead with a controller so that water flow can controlled in order to provide bursts of current. Constant, strong water flow is not desirable for fish, substrate or plants or corals.

The last aspect of water chemistry to consider before selecting fish livestock is the level of nutrient export capabilities of the filtration system. Modern wet/dry filters, canisters and even bio-wheel power filters are cable of breaking down toxic compounds like ammonia and nitrite very efficiently. However, what is left over is nitrate, which over time can build up to high levels. High levels of nitrate will cause stress and reduced overall health to many fish species; as well as, promote nuisance algae growth and overall poor water conditions.
While water changes using clean RO/DI based saltwater can reduce nitrate levels, hobbyists will ultimately need to employ filtration methods specifically designed to export or reduce the nitrate levels in the aquarium. In order to keep fish that are considered moderate to difficult to keep, hobbyists will need to employ one or more of the following nutrient export filtration techniques: protein skimming, frequent water changes using RO/DI water and a quality salt mix, large quantity of live rock, sump with fast growing live plants or an algae scrubber solution. Any of these nutrient export solutions can be effective at keeping water quality high and dissolved nitrates low; however, the use of more than one of these techniques at the same time is recommended as they are much more effective when used together.
  Filtration System
As you can probably guess from the water chemistry section, filtration systems have a huge impact on keeping quality water and determining the overall fish load an aquarium can support. Since this guide is specific to fish stocking in a marine aquarium, we will only discuss filtration as it pertains to fish stocking levels. All saltwater fish aquariums will require mechanical filtration, biological filtration and good internal water flow, with water flow affecting both for dissolved oxygen and to assist the mechanical filtration with removing solids. Marine aquariums with light to moderate fish stock levels, which translates to about 1 inch of fish per 5 gallons of water can be successfully maintained by using either a high-end bio-wheel power filter, high-end canister filter or wet/dry filter, combined with powerheads for internal water movement and regular water changes. Adding live rock and a protein skimmer can increase the fish load to 1 inch of fish per 3 gallons and extend the time between water changes.
While the further addition of a sump with live plants or an algae scrubber for nutrient export can further increase stocking levels to 1 inch of fish per 2 gallons of water volume. All fish stocking recommendations are based on a tank that is fully cycled and biologically mature. When a tank is first established and the beneficial bacteria are just forming, it is important to move slowly with fish additions and test the water every few days. Weekly water changes and a reduced feeding regimen will also help take the load off of a maturing filtration system. With all new tank setups, fish should be added slowly with one or two fish being added every 2 to 3 weeks, which will allow the filtration system and beneficial bacteria to adjust to the increase in waste products.

After an aquarium is fully mature (approximately 1 year) hobbyists can utilize combinations of filtration techniques and water changes to increase fish loads above what is recommended here. Many factors come into play when giving advice on the fish load an established aquarium can support; however, always remember to work with nature and provide the proper environment to support the nitrogen cycle and move slow to allow beneficial bacteria to do their work. Hobbyists who maintain high levels of dissolved oxygen through laminar water flow, use live rock and live sand, utilize protein skimmers, use sumps for plant or algae nutrient export and last but not least use a RO/DI unit to provide quality water for top off and water changes, will find that keeping a marine aquarium does not have to be difficult and is very enjoyable.
  Fish Compatibility
Fish Compatibility as it pertains to stocking levels in an aquarium is more than just fish fighting with one another. Of course if incompatible fish are kept together their constant fighting will likely mean that some fish will become stressed and likely get sick and die. However, another factor of fish compatibility involves available territory within the aquarium. While a number of marine reef fish like Chromis, Anthias and some Tang species will readily school together within the aquarium, most reef fish attempt to stake out territory within the aquarium.
This territory is usually based on feeding habits and shelter, where fish will look for an area within the aquarium that has good caves and crevices in which to retreat to when threatened and in which to sleep, and where they can readily find food to eat. Problems occur when fish are kept together and they see one another as competition for both food and shelter. An prime example of this is keeping multiple dwarf marine angelfish in small to medium sized aquariums, they will both try to claim either the entire tank or most of it as their territory, where often the loser is marginalized to one small area of the tank or simply becomes stressed, becomes ill and dies. Unless you have a very large aquarium (hundreds of gallons) it is very important to keep fish species who will not compete with one another and are accepting of sharing the same territory or space within the aquarium.

  Fish Size & Swimming Habits
The adult size of each fish and how much room they need to swim comfortably within the aquarium ties into the overall compatibility and ultimately the health of aquarium livestock. In general, fish species that grow larger like Angelfish, Triggerfish, Groupers, Surgeonfish and others are typically more aggressive than fish species who only grow a few inches in length. This directly effects the amount of space they need to feel comfortable within the aquarium. While smaller fish are happy to hang out near a rocky crevice or swim in a school with others of their species, larger more aggressive fish will want to claim a larger area of the aquarium and will generally not tolerate any other fish they see as competition for food or dominance. Also in the case of some fish like fast swimming open water Surgeonfish, Sharks, Rays or other similar species, their unique size and swimming habits may make them less suitable to be kept with other smaller or more shy fish species. Ultimately, fish stocking is more than just a calculation of inch of fish per gallon or employing the best filtration systems, it is a balance between fish, their tank mates and their aquarium environment.
  In Conclusion
Make sure you have a good understanding of the Nitrogen Cycle and how it works in an aquatic environment, utilize the best combination of filtration systems that you can afford. Be sure to cover the basics, breakdown or remove waste products, provide plenty of dissolved oxygen, export nutrients from the aquarium and provide fresh water and beneficial trace elements through water changes. And remember go slow, during the first six months to a year, give time for your filtration system to catch up each time you add new fish (usually 2 to 3 weeks) and do your best to recreate the methods mother nature uses. By providing high oxygen levels, biological filtration, protein skimming, proper color temperature (10k - 20k) lighting, controlled additions of new tank mates and keeping in mind the adult size, compatibility requirements of new specimens and you will guarantee yourself many years of successful marine fish keeping. Good Luck!

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