What is aquaponics?

Answer: most simple definition is that it is the marriage of aquaculture (raising fish) and hydroponics (the soil-less growing of plants) that grows fish and plants together in one integrated system. The fish waste provides an organic food source for the growing plants and the plants provide a natural filter for the water the fish live in. The third participants are the microbes (nitrifying bacteria) and composting red worms that thrive in the growing media. They do the job of converting the ammonia from the fish waste first into nitrites, then into nitrates and the solids into vermicomposting that that are food for the plants.

In combining both systems aquaponics capitalizes on the benefits and eliminates the drawbacks of each.

How many months the system will develop?

Answer: Cycling starts when you (or your fish) first add ammonia to your aquaponics system. Ammonia (chemical formula NH3) is a compound made of nitrogen and hydrogen. It can come either from your fish or from other sources. Ammonia is toxic to fish and will soon kill them unless it is either diluted to a non-toxic level or converted into a less toxic form of nitrogen. In addition, nitrogen in the ammonia form is not readily taken up by plants, so no matter how high the ammonia levels get in your fish tank; your plants will not be getting much nutrition from it.

The good news is that ammonia attracts nitrosomonas, the first of the two nitrifying bacteria that are present in the air and will populate the surfaces of your system. The nitrosomonas bacteria convert the ammonia into nitrites (NO2) (the golden line in the chart above). This is a necessary step in the aquaponics cycling process; however, nitrites are even more toxic than ammonia! But there is good news because the presence of nitrites attracts the bacteria we are truly after nitrospira (shown by the green line in the graph below). Nitrospira convert the nitrites into nitrates, which are generally harmless to the fish and excellent food for your plants.

Once you detect nitrates in your water and the ammonia and nitrite concentrations have both dropped to .5 ppm or lower, your system will be fully cycled and aquaponics will have officially begun!

How many fish I am allowed to have in my fish tank?

Answer: Again this will depend on whether the system is a commercial or backyard system, with the commercial systems requiring the correct amount of fish and plants for optimum production. The more fish there are in a system, the more nutrients there are for the plants to consume, but if there are not enough plants to consume these nutrients, the excess build up in the water can cause the fish to suffer. As a general rule, backyard systems can stock between 10 – 30 kg of fish per 1000 liters of water.

Having a test kit is really important for aquaponics?

Answer: Testing kit is very important, this will tell also where you are in the aquaponics cycling process – typically a four to six week endeavor. Specifically, you must monitor ammonia, nitrite, and nitrate levels as well as pH so that you know that all these elements are “in range”. If they are not, you may need to take corrective action. This is also the only way that you will know when you are fully cycled and ready to add your fish. Plus, watching the daily progress of the cycling process is fascinating and something you can only see through the lens of a test kit. By the way, once you reach the point that your system is fully cycled, you will need to do much less monitoring than during the cycling process. So get through the cycling process and look forward to reaping the fruits ( or should we say the “fish”) of your labor.

To do their testing, most aquaponic gardeners use a product by Aquarium Pharmaceuticals Inc. called the API Freshwater Master Test Kit. This kit is easy to use, is inexpensive, and is designed for monitoring the cycling process in fish systems.

What water pump do I need to use?

Answer: Much like water pumps, air pumps work harder and use more energy the deeper that the stone diffuser is placed in the water. Purchasing a quality air pump, preferably with battery backup, ensures that the fish are always kept up to good levels with oxygen availability. Air pumps usually have performance graphs much like water pumps. Make sure that you will be getting the air flow that you desire at the depth you will be using the stones / diffusers.

What is different raft and grow bed system?


In a raft system (also known as float, deep channel and deep flow) the plants are grown on Polystyrene boards (rafts) that float on top of water. Most often, this is in a tank separate from the fish tank. Water flows continuously from the fish tank, through filtration components, through the raft tank where the plants are grown and then back to the fish tank.

The beneficial bacteria live in the raft tank and throughout the system. The extra volume of water in the raft tank provides a buffer for the fish, reducing stress and potential water quality problems. This is one of the greatest benefits of the raft system. In addition, the University of the Virgin Islands and other research programs refined this method during 25 years of research.   Nelson and Pade, Inc. utilizes the raft method as the base of their highly productive Clear Flow Aquaponic Systems®.

In a commercial system, the raft tanks can cover large areas, best utilizing the floor space in a greenhouse. Plant seedlings are transplanted on one end of the raft tank. The rafts are pushed forward on the surface of the water over time and then the mature plants are harvested at the other end of the raft. Once a raft is harvested, it can be replanted with seedlings and set into place on the opposite end. The optimizes floor space, which is especially important in a commercial greenhouse setting.


NFT (Nutrient Film Technique) is a method in which the plants are grown in long narrow channels. A thin film of water continuously flows down each channel, providing the plant roots with water, nutrients and oxygen. As with the raft system, water flows continuously from the fish tank, through filtration components, through the NFT channels where the plants are grown and then back to the fish tank. In NFT, a separate bio filter is required, however, because there is not a large amount of water or surface for the beneficial bacteria to live. In addition, the plumbing used in a hydroponic NFT system is usually not large enough to be used in aquaponcis because the organic nature of the system and “living” water will cause clogging of small pipes and tubes. NFT aquaponics shows potential but, at this time, it is used less than the other two methods discussed here.

Media-filled bed

A media-filled bed system uses a tank or container that is filled with gravel, perlite or another media for the plant bed. This bed is periodically flooded with water from the fish tank. The water then drains back to the fish tank. All waste, including the solids, is broken down within the plant bed. Sometimes worms are added to the gravel-filled plant bed to enhance the break-down of the waste. This method uses the fewest components and no additional filtration, making it simple to operate. The production is, however, much lower than the two methods described above. The media-filled bed is often used for hobby applications where maximizing production is not a goal.

When do I need to change my water in my AP system?

Answer: You don’t have to change your water every time, old system is much better. But in case you have a high ammonia that’s the time you need to change your water. We all know that higher level of ammonia can harm your fish.

What is the feeding rate I need for my fish?

Answer: We have the feeding guide for fish, but in aquaponics we have to consider and monitor the ammonia level. If you are cycling your system with fish, feeding should to be kept to an absolute minimum during the first 1-2 months. Only feed the fish what they will consume in 5 minutes – no more than 1 tablespoon per 20 fish per day. If your aquaponics fish don’t seem to be hungry don’t feed them. Fish can survive for weeks without feeding. Your water will probably go green for some weeks, don’t worry.

Once the water in your aquaponics system becomes clear you may gradually increase feeding levels, again paying attention to how much the fish consume in 5 minutes. You can also start feeding your fish two or three times a day. As a guideline, mature tilapia typically consume about 1% of their body weight in feed a day, while fingerlings can consume as much as 7%.

Do I need additional nutrients aside from the water run into our system?

Answer: There are 16 plant nutrients- three of them are non mineral, and thirteen are mineral. The three non-mineral nutrients are pretty obvious and are not really supplemented by growers except in the form of water (and in some cases) carbon dioxide.

These non-mineral nutrients are:

Oxygen, O
Hydrogen, H
Carbon, C

Like everything on earth, plants are carbon based life and a majority of the plant structure is composed of carbon chains (with hydrogen attached) and water.


Water is relatively cheap in nature, so plants use water to support themselves.  Instead of making very thick, tough cells that can stand on their own, many plants build rigid cell walls and then pump their cells full of water- like a balloon to build structure.

Plants are great at maximizing growth with the least expensive resources.  Not only is water (Hydrogen and Oxygen) a useful building tool on it’s own, but plants have the amazing ability to break water apart, scrapping the oxygen, and using the hydrogen for all sorts of things, including hydro-carbon chains.  Basically, water is used as a molecule, but is also broken by the plant to use for spare parts.

Mineral Nutrients

When we think of plant nutrients, we usually think of mineral nutrients- these are what are commonly supplemented by growers in the form of a fertilizer, manure, compost, or other organic nutrient addition.  Many of them are also available or unavailable in the soil, depending on where you live and what kind of soil you have.

By and large, mineral nutrients can be a bit fussy, and just because they’re present in your system doesn’t mean they’re available.

Lots of different things influence whether mineral nutrients are available, but the most important thing is pH.  Some minerals are only available at higher pH values, but more are only available at low pH values.  This can make the lives of aquaponic growers pretty difficult at times.

When a nutrient is present in your system, but not available, usually that mineral is what we called “precipitated out of solution.”

Basically this means that instead of being dissolved in the water in the system, the nutrient becomes a solid and usually settles on the bottom of the tank, or attaches to a piece of gravel, or other surface in your system.

This means that while the nutrient is technically there, it’s not available for the plant to take up.

The best example of this is iron.  Iron is often present in aquaponic systems, however, because of system pH and dissolved oxygen, it typically isn’t very available to the plants.  Instead, it often exists as a solid precipitate in the system.

So, it’s important to know what nutrients are necessary for your plants and how to make them available in your system.

Mineral Plant nutrients are divided into three groups- Primary Plant Nutrients, Secondary Plant Nutrients, and Micronutrients.

The Primary Plant Nutrients are:

Nitrogen, N
Phosphorus, P
Potassium, K

These are the most consumed nutrients, and are the three concentration numbers on fertilizer labels: N – P – K

The Secondary Plant Nutrients are:

Calcium, Ca
Magnesium, Mg
Sulfur, S

These are most commonly supplemented in aquaponic systems that use pH raising nutrient supplements to moderate pH- primarily Calcium and Magnesium in the form of agricultural lime, a hydroxide composed of Ca and Mg.

It isn’t necessary to supplement sulfur in most systems, but it is commonly supplemented in neutral or high pH system if growers use Epsom salts (magnesium sulfate) or potassium sulfate.

The micronutrients are:

Copper, Cu
Zinc, Zn
Boron, B
Molybdenum, Mo
Iron, Fe
Manganese, Mn
Chloride, Cl
Of these micronutrients, Iron is most common in aquaponic systems.

Copper is commonly included at high enough levels in the feed.

Zinc is common in fish feed as well as the galvanized steel components that inevitably make their way into our systems (despite our best efforts to exclude them!).

Boron is required at low enough levels that the levels existing in most system are sufficient (Although I have been known to drop a pinch of borax soap in my system every 9 or 10 months).

Molybdenum is also required at low levels, to the extent that all of the Molybdenum a plant needs for it’s entire life can often be found in the seed that it germinated from. (It’s only after growing some plants for several generations in a Molybdenum free environment that the deficiency occurs!)

Manganese is seldom deficient, and chloride commonly enters the system in the fish feed, and in the form of salts.

All of these are necessary for plants to grow and be healthy, and so, over the course of the next year, we’ll dig in and talk about each of these important plant nutrients in detail- including how to manage them in your system, adding them to the system, recognizing deficiencies.

What quality of water do I need in my system?

Answer: As with all water used in Aquaponics systems, it has to be free of toxic chemicals, and if possible, have little or no suspended solids (clay). Water that is clear will make it easier to observe the fish, giving you a clear view of what is happening in the fish tank. Clear water allows you to monitor any buildup of wastes at the base of the tank, as well as letting you see that the fish are eating all of the food given to them. If using chlorinated water, chlorine must be removed before water can be added to the system. Chlorine can be removed from water by either using a filtration unit, exposing the water to air and sunlight for several days, or using water additives that neutralize the water.



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