Five Mistakes to Avoid in Your First Aquaponics System


DWC Aquaponics LettuceHey Trifecta fans.

This week we are covering five mistakes to avoid making in aquaponics. Aquaponics may seem daunting the first time you learn about it. The idea of having to maintain the health of both a fish and plant environment can seem like a lot to take on.

However, aquaponics is relatively simple to set up and maintain. In fact, so long as you be sure to avoid making these all to common mistakes you’ll be sure to avoid the headache others have experienced when starting out and be off and running in no time. So lets dive right in!

What are the five mistakes to avoid making in aquaponics?

#1: Duckweed

The number one problem we see with new growers and with those interested in aquaponics is the use or the recommended use of duckweed. I once was one who fell into this trap in my first system. Yes fish, specifically tilapia, will eat duckweed with gusto, and yes the duckweed will repopulate faster than the fish can eat it. It’s this info that makes it very attractive as a feed to fish to aquaponic growers. We’ve even seen claims that duckweed is around 40% protein and that it is perfect diet for those trying to grow a high protein fish.

Let’s clear the facts on this note. Duckweed is 95% water. This can be confirmed by a simple google search. When dried, duckweed does contain somewhere between 35-40% protein. Most of those that are advocating duckweed are unaware that the 40% protein figure they claim is for dry duckweed. Your fish in aquaponics systems are not eating dry duckweed. Your fish are eating wet duckweed which as I stated at the beginning of this paragraph is 95% water which means that the protein content of duckweed is 35-40% of the remaining non water portion of wet duckweed.

So wet duckweed (what your fish eat) is only about 2% protein. THIS is why fish eat it so ferociously, it is because they are starving. This is especially true of growers who try to rely solely on duckweed and don’t provide any supplemental nutrition to their fish. Couple this with the fact that duckweed grows faster than your starving fish can eat it. The growth is unstoppable and this is a problem. It gets out of the fish tank and into your pipes, grow beds, sump, pumps etc.

It is unruly and can cause a major headache. If you are interested in growing food for your fish look into black soldier fly larvae. They provide more protein and won’t clog your pipes and pumps like duckweed will.

#2: Having too many fish in the tank

Aquaponics Aquaculture Tank
Too many fish can be a bad thing.

Another common problem among those starting out is that they want to grow as many fish as possible as quickly as possible. The problem with this is that they overcrowd their fish tanks resulting in stunted growth for the fish and high nitrate levels also affecting the health of the fish.

When starting out with a system for the first time keep your stocking densities low. I’d recommend one pound of fish for every five gallons of water in your fish tank. This is lower than the generally accepted densities but from our experience low densities do not hinder plant growth and over the lifetime of the system create a more stable system.

In addition it will save you money in feed which can add up over the lifetime of your system. Unless you are growing on a large commercial scale it is highly unlikely that the fish portion of your system will be profitable. As a small scale or hobby grower you should be looking to keep the fish side of the operation as low as possible to maximize your margins. Don’t make the mistake of over-stocking, you can always add fish later, it’s a waste to stock too densely lose fish to death or have to take them out.

#3: Using tap water in your system

This is one of the biggest mistakes of first time growers in their aquaponics systems. Most of the cities in the US add chlorine and fluoride to their water. Specifically chlorine can be deadly to fish. If the only access to fresh water you have is through your tap you need to “off-gas” the water before letting you fish come in contact with it. When setting up a brand new system you can do this by adding the water to the fish tank and letting it sit for 48-72 hours with the aeration unit going.

If you have a running system and need to add water to it, you need to off-gas it before you add it to the system. When public utilities are your only access to water it would behoove you to keep a steady supply off-gassed in case you need to add water to your system.

#4: Media

Another common mistake new-comers make in aquaponics comes in choosing their media. The issue with almost all media is that they will affect your ph in some way, at least initially. For instance, we use expanded shale in our systems. This expanded shale raises our ph, in our large systems it generally raises it .5-1ph. This initial raise can affect the health of plants and fish and for that reason we don’t add either until a few days after the shale is added. Over the course of about 6 months the ph lowers slowly back to an acceptable range for both the plants and fish.

We are willing to use the shale because we can get it locally and it is readily available in large quantities. Other suitable options include hydroton and lava rock. One example of unacceptable media is limestone. Limestone affects the ph in an irreversible manner and will affect the health of both the fish and the plants. While it is attractive because of its availability and cheap price tag it is not suitable for aquaponics operations.

There is a quick test to see if the media you picked affects ph. First start by testing the ph of your water. Second, add water to a cupful of media and test the ph of that next morning. If it has changed significantly you can be certain that your media will affect the ph of your system.

#5: Using harmful additives to lower the pH

There is too much emphasis on ph in aquaponics in my opinion. These are systems of relationship and balance. Generally speaking a high ph will lower over time gradually. In mistake #4 to avoid I mentioned how it takes 6 months for our ph to drop due to the media we use.

Some people are impatient and resort to using chemical such as muriatic acid to lower their pH. Chemicals will lower your pH but they are largely untested in aquaponics. We know many of them will harm the health of your fish and plants. If you are considering chemicals, don’t. It is that simple. The pH of your system will drop on its own over time due to nitrification, and that gradual drop is safe for your fish. In addition, fish and plants are more tolerant than we give them credit for. So you don’t need to be that rash with the use of chemical alterations. The only option that I would recommend is the use of vinegar. You have to be careful here too as too much will affect the health of your fish.

Small sustained applications however will lower your pH over time. Just be careful use small amounts (like ⅓ cup for 500 gallons small) and monitor the situation. Vinegar is a slow fix, be patient and keep the additions small.

So there you have it.  Five mistakes to avoid making in aquaponics because now you know better. Obviously there are more than five mistakes to avoid making in Aquaponics. That’s why part of learning and becoming an aquaponic gardener is going be trial and error but you can be sure to avoid big blunders by skipping the five mistakes to avoid making in aquaponics listed here. So no more delaying it’s time to go out and try it out yourself!

The Trifecta Team


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