When I first started my aquaponic journey some 10 years ago, I was told and retold that I wouldn’t really be an expert, wouldn’t really understand what I was doing until I had killed a bunch of fish. I wish I could say those prophetic voices were wrong, that I listened and learned and followed the wisdom of all the resources that are out there. But the truth is if you start to look around, there’s not as much information as you might think, and a fair amount of it is contradictory. What one book or web site tells you, another disagrees and says something else.

Combine this with the reality that we people are artistic at heart. We want to create and discover. Sometimes we say it is learning the hard way. But it is also being changed by the learning process. A book might teach you best ways to manage a tank of fish, might tell you how to be a farmer. But holding a wriggling fish in your hands, testing water quality, measuring food quantities – these things don’t teach you about farming. They make you a farmer. And that process that makes you a farmer will empower you to grow fish, vegetables, and to be a part of cultivating life itself, even if you don’t know every minute technical detail. So if you are serious about raising fish, then having a basic understanding of the fish system is critical. The question for each of us is whether we want to know about farming, or whether we want to go out and become a farmer.

The fish system begins with water. You have to have good water. Water is the life giving bio-environment on which the fish depend. Before you set up your fish system, you should have your water tested. The water may come from a municipal source, a well, ground water such as a river, lake, or pond, or even from rain water collection systems. There are competing schools of thought regarding water treatment. Some people think the water needs to be some form of perfect. Some think you should customize your water based on testing data and the specific needs of the fish. Some people suggest whatever the water is, find a fish that can live I it and use that. Let’s weave it all together and find a sensible and manageable middle ground.

There are some things which will hurt any fish, and you need to be aware if those elements are present in the water. Some examples are lethal elements are chlorine or high levels of copper. High levels of iron can also affect a fish’s ability to process their food, so the water can seem fine, yet the fish won’t seem to grow or be as healthy as you would expect. (I learned this one the hard way!) All of these issues are easily treatable, but they do require awareness. Also, if you have these kinds of issues, consider how you might access some other less fish toxic water source. 

Dealing with these types of issues is generally best done before the water makes it into the fish system. Depending on the water issues, both ionic-exchange pre-filtration and simple flow through filters can remove virtually any unwanted element. Remember, the system houses a lot of water. The initial set up and filling requires many gallons. But once it is up and running, these systems have extremely low water usage, and do not require large amount of new water input.

The technical term for the particular type of fish system we are discussing is a Recirculating Aquaculture System. This type of fish system constantly reuses the water, so it is extremely efficient. However, this requires the water to be constantly cleaned or the fish will die from their own wastes. The two sources of fish waste are their feces and their breathing. Keeping the water clean from these sources requires the continuously circulation of the water through a series of filters.

Feces Filtration

Fish feces is a solid. If left long enough in the water, it will eventually dissolve into the water. Like any living creature, residing in its own feces will eventually cause disease and death. The solution is to remove as much of the solids as possible, as quickly as possible. This is why the first stage of the circulating system is a solids filter. Common types of solids filters listed from last to most effective include swirl filters, radial flow filters, plate filters, bead filters, and rotary drum filters.

Swirl and radial flow filters are used and discussed a lot in backyard Do It Yourself type systems. They are relatively easy to make using easily attainable 50 gallon barrels, and they get enough of the waste out to allow reasonable operations as long as fish density is kept to a minimum. They are not effective when stocking significant densities of fish.

Plate filters are quite effective at removing solids. They work by slowing down the water causing it to drop the waste, as well as running the water through a mesh screen which blocks the passage of any solids. They are relatively inexpensive to build. The negative to these filters is they require regular cleaning of the screens and flushing of the filter tank, which must be done manually, so they are quite labor intensive. And as with any of the filters, if the waste is not removed from the tank in a regular, timely, and thorough fashion, the water quickly becomes contaminated.

Rotary drum filter were developed for the commercial aquaculture industry. They are extremely efficient, and self-cleaning. Essentially the water flows through a fine mesh screen. As the filter catches waste it allows less water to flow through raising the water level in the tank. Once the tank reaches a certain level, a sensor trips a relay which simultaneously opens a drain line, turns on a high-pressure water spray, and rotates the drum, thereby thoroughly cleaning the screen. Because of the automation and regularity of cleaning, finer screens can be used in these filters. They provide exceptional solids filtration available for recirculating aquaculture systems. They are not extremely complex, but they are somewhat more involved to manufacture, and as such they carry a higher price tag, as well as having the highest energy usage of the filter options. Drum filters are the most used solids filters in the commercial aquaculture industry for their effective removal of large amounts of solids waste.

The final solids filter to mention is the bead filter. Bead filters carry the most potential for aquaculture use. They are relatively simple to manufacture, they can provide exceptional filtration when properly configured, can be plumbed for self-cleaning, they are very low energy users, and can also provide an element of biofiltration within the process. Not all bead filters have been successful, but when well engineered, we believe they may well be the best filtration option, and is the standard filtration option provide with our aquaponic systems.

BioFiltration

The second toxic waste that must be addressed is simply the breathing of the fish. If a person was to put a plastic bag over their heads and breath continuously, they would in a relatively short time use up all the oxygen, grow sleepy, and eventually die from carbon monoxide poisoning, which is lethal to humans. Fish have the same problem. They breath oxygen out of the water, and exhale ammonia through their gills into the water. Different types of fish have different capacity to survive in toxic water, but eventually this ammonia build up will get to the place where it will kill the fish.

Thankfully, God placed a natural solution in nature in the form of what are called nitrifying bacteria. There are two types of bacteria which make this purification process possible. The first turns the ammonia into nitrite, which is still toxic to the fish. The second turns the nitrite into nitrate, which the fish are not bothered by, and which, when we get to the plant side of the equation, is the very thing plants need for food to grow.

A biofilter is essentially a container housing a media on which these bacteria can grow. As the water flows through the bacteria consume the toxic ammonia, and leave the water both fish and plant friendly. There are several specialized media used for this purpose, as well as shredded pvc, or even polypropylene embossed strapping. The point is to use a media with lots of surface area for the bacteria to live.

(Note: media and wicking beds in the plant system also provide homes for nitrifying bacteria. Some aquaponics designers utilizing coupled systems do not add any additional filtration and spend a lot of time discussing the importance of balancing your system This essentially has to do with making sure you have few enough fish to not overwhelm your bio-filtration. It is much more efficient to simply add additional filtration which allows you to increase fish growth to the optimum levels of the fish system without overwhelming the plant system.)

From there the water returns to a sump where it is pumped back into the tank to repeat its journey. On that return line several additional items can be included as needed. A carbon filter is a flow through filter that will remove bad smells, chlorine, and can help balance some hardness issues. A peat filter is sometimes used in cases where water is excessively alkaline. Peat is a natural substance that is quite acidic. So a flow through peat filter can help lower the ph. However, remember that most fish like a somewhat higher ph, and over time the system will actually balance itself. We have used peat filtration in particular circumstances, but not found it necessary for long term use. Lastly a flow through UV filter exposes the water to UV rays which purify the water from any harmful bacteria traveling with the water, as well as killing any algae that is moving through.

The final element of the fish system is aeration- putting air or oxygen back into the water for the fish. The amount of dissolved oxygen in the water is probably the most essential element in determining fish stocking densities, and as such an entire article has been designated for that discussion. Learn about aeration here.

While all of this may seem a bit complex, it is really quite simple. When I began, I found myself trying to bypass different parts of the system to save money, or because I read some article that it wasn’t needed. In some cases it isn’t needed. But if you actually want a safe and easily manageable system that can stock market viable quantities of fish, it is worth the time and effort to include every element of the system.

Take a look at our fully designed fish systems.