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 Post subject: Fish to Water Ratios
PostPosted: Mon Mar 21, 2011 9:41 pm 
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This is the fifth in a series of posts that are going to teach you much of what you need to know about Aquaponics. So, if you’re curious about the most amazing food growing technology on the planet today, watch for this series of educational posts on Aquaponics and please, become interactive by making comments or asking questions.

In Part One, “The Process”, I wrote about what Aquaponics is and why it is important to Preppers (those preparing for what is about to come down the pike), the fact that you can grow food for you and your family year round as long as your Aquaponics system is in the proper environment. I also gave a description of the biological processes involved that make Aquaponics work.

In Parts Two and Three, “The System”, I wrote about the components of a basic system. To quickly review, I wrote about the need for a bio-filter and that it is usually combined with the grow bed to form a single Aquaponics component called the grow bed, which is the most important part of an Aquaponics system. I told you about the grow bed media, the grow bed shape, and that you need about one gallon of grow bed/bio filter volume for every gallon of fish tank volume and the reason for this ratio. I discussed the need to flood and drain your grow beds four times an hour and how to properly size your water and air pumps.

In Part Four, “System Startup”, I talked about an Aquaponics system water and all the important aspects of the water like the DO (dissolved oxygen), nitrites, nitrates, pH and alkalinity. I talked about how to measure the water using a freshwater test kit, TDS meter, a DO meter and a pH meter to determine that it’s safe for the fish and the plants. I also explained how to get an Aquaponics system started and how to “cycle” your system.

I’m now going to focus on the amount of fish you can grow in your Aquaponics system; but I’m only going to discuss the most popular fish, Tilapia, among Aquaponics farmers because that’s the species with which I’ve had experience.

I going to tell you about an important item that needs to be addressed, the ratio of fish to water. There are a number of fish to water ratios being given out by Aquaponics enthusiasts. So, let me start by giving you the ratio of 3 gallons of system water for every pound of Tilapia as a maximum density of fish to water. As a beginning Aquaponics farmer, I recommend stay at or above 5 gallons of water per pound of fish. But this is not the most important number in determining how many fish you can raise in a given system. Please, let me explain.

This is the number we have in our systems in our greenhouse. Our systems have a total of three 120 gallon fish tanks and a total of five 11 square feet of deep (12″) media grow beds, as we didn’t have room for a 6th grow bed to balance it out.

We recirculate the water between the three fish tanks so it acts like a 360 gallon fish tank in its biological stability. What we found as the fish grew out and are now average about 1.75 pounds each, is that the 55 square feet of 12 inch deep media grow beds adequately convert the fish waste (including solids – without accumulation), into plant nutrients. We add heterotrophic bacteria weekly to help with the solid waste mineralization and for water clarity.

Our current system has a total of about 330 gallons of water in it and about 55 pounds of Tilapia for a gallons of water to pounds of fish ratio of about 6:1.

With an increased amount of bio-filtration (more grow beds), it may be possible to decrease the water to fish ratio to a lower gallons of water per pound of fish. With a decrease of bio-filter volume then this ratio must be increased. This is based on feeding the fish as much as they will regularly eat and as often as is practical with no food left in the tank.

Another way to increase the fish density is to decrease the amount of food given to the fish. This will slow their growth, which may be desirable once they are fully grown. In any event, the real ratio here has to do with the amount of food digested and the size of the bio-filters needed to process the waste.
 As can be seen, the pounds of fish the system can support is more a function of the amount of bio-filter volume available than it is to fish tank size. This assumes proper design and selection of other system components.

We have found that the best way to regulate and insure that the fish are fed portioned amounts of food and on schedule is to have an automatic fish feeder. The feeders we use have an eight event per day timer and can be set to dispense food in one second intervals. By setting the timer to dispense food for ten seconds, three to four times every day, which is about every three hours, we know that the food they receive is the same every day. This allows us to adjust the amount of food given the fish as needed and it also allows us to leave for a few days without worry that they won’t be fed. As the fish grow out, we increase the number of seconds on each feeding, thereby giving the fish more food. We highly recommend using an automatic fish feeder.






As the sun crosses the equator, we change the number of feedings per day. In the spring and summer, the days are longer supporting up to 4 feedings every three hours, as verses 3 feedings in the fall and winter. This allows for more food and, therefore, waste in the system. Couple this with warmer water temperature, and we have a faster fish growth rate as well as more nutrients available for the plants. The warmer water also contains less dissolved oxygen (DO), which is problematic. The warmer water can also be less conducive to plant growth.



Another way to increase fish density is to remove the fish waste solids from the system. This would un-tax the system from the need of some of the DO (dissolved oxygen) in the water and would reduce the amount of system ammonia; but it would also reduce some of the resulting nitrates. In addition, this would remove some valuable plant nutrients that are a result of the mineralization process of fish solid waste. So, we leave in the fish solids, add heterotrophic bacteria weekly (see Aquaponics 101 Part Four: System Start Up) and provide ample aeration.

Through the process of solid waste mineralization, the nutrients and minerals found in the fish food makes their way into the plants. So, what you feed your fish is what you feed your plants.

The key to this all working is adequate DO (dissolved oxygen, see Aquaponics 101 Part Four: System Start Up) in the water. As we measure it weekly, we have changed our system design over time to improve this important factor. Because the fish waste conversion to plant nutrients requires ample DO, we have a DO meter; and in using it regularly, along with other water chemistry measurements, we learned about the system dynamics as it matured.



As our fish grew out and we increased the amount of food we gave them, the DO in the water decreased over time, which affected the nitrification process. DO is also a function of water temperature and this must be accounted for in making DO measurements. We then added aerators to our grow beds and also increased the aeration in the fish tanks. The DO then increased to a good level for the mineralization of the fish waste solids and the nitrification of the ammonia in the system.

Once the ratio of fish pounds to water gallons reached about one pound of fish for every four gallons of water we noticed the pH of the water dropping below the optimum of 7.3 ppm (mg/L). As the fish continued to grow, the pH found its way down to as low as 6.0 ppm during the winter as we were injecting CO2 into the greenhouse. The CO2 found its way into the water by way of the aerators and when combined with the Hydrogen released by the bacteria in the nitrification process, carbonic acid was created. This is the normal process for an aquaponics system and is the main reason the pH will decrease as your fish grow out and you slowly increase their feed. Reducing the CO2 pumped into the fish tank and grow bed by pulling in outside air helped and brought the pH up a few tenths but that was not enough.

With the pH dropping below 7.0, the bacteria stopped reproducing and the ammonia levels started to climb. Water exchanges were an immediate fix but not a long term solution. Adding in more bacteria and Potassium Hydroxide (KOH) to the system brought the pH back up to 7.3 ppm and the ammonia levels soon went down to safe levels.

After about three plantings and many grown out flowering plants, the potassium had been mostly depleted from the system. The flowering plants stopped producing, leaves turned yellow and the cucumbers went from green to white. We have added chelated iron along with the potassium and are looking forward to green leaves and cucumbers.



A eleven square foot, deep-media (12″) 70 gallon grow bed holds about 36 gallons of actual expanded clay volume and 30 gallons of water. This includes about one inch of expanded clay above the highest water line to prevent algae growing on top of the expanded clay and mold growth on the leafy green plants bottom leaves.

 This gives about 60 gallons of wetted grow bed media being used as a bio-filter.

A two, 11 square foot deep-media grow bed system can support about 20 pounds of fish maximum with ample fish tank (120 gallons) and grow bed aeration, and works out to about 6 gallons of bio-filter/grow bed volume per pound of fish. Again, this one pound per six gallon of bio-filter number is a maximum and is only for a mature system, one that is at least one year old. Keep it safe and stay below one fish pound per six gallons of useable bio-filter.

Using the above ratio of 6 gallons of grow bed media per pound of fish we then get the following:



Grow Bed sq ft…….Fish Tank Gallons….Media Gallons…….Pounds of Fish



2X11′ Beds……..……………120…………………120………..……….20


4X11′ Beds……….………….320…………………240………..……….40


5X11′ Beds……….………….320…………………300……….………..50


8X11′ Beds…….…………….610…………………480……….………..80


10X11′ Beds…..……....…....610…………………600……….……...100



It is important that the grow beds all be of the flood and drain (ebb and flow) design. This allows for the bacteria on the surface of the Hydroton and vegetable roots to be aerated between the drain and flood cycles. Even with added grow bed aeration, which adds additional DO to the water, it does not reach all of the bacteria or vegetable roots as well as does draining and re-flooding.



The pounds of fish column in the above table is a maximum total in the system. As the fish grow out, they do so at different rates and you need to plan ahead for the maximum size they will be before harvesting. If you do not plan on harvesting your fish and choose to keep them in the tank for their life, then you need to plan on the maximum poundage of each fish when fully grown. Breeding your fish for sustainability is another option you may want to consider.



It is important to note the difference between maximum fish poundage and yearly pound production. Tilapia (as with most fish species) tend to grow faster in warmer water with longer daylight hours, natural or artificial. It is possible with certain Tilapia species to grow to market size (1.25 pounds) within 6 months. This would give you two crops of fish per year in a single tank thereby doubling the maximum poundage numbers to get annual yield poundage.



This brings up the concept of system design. A system is designed for either maximum fish growth or maximum vegetable growth, but not both. Keeping your fish water warm and removing fish solids is a method of maximizing fish growth and are some of the techniques used in aquaculture, as is adding pure oxygen to the water. However, warm water is often not conducive for good vegetable growth. These and other factors determine what it is that you will accomplish in your system.

As always, monitoring your water quality regularly, adjusting the amount of feed given the fish and adjusting your pH to maintain that quality is important.



We have added some fingerlings to one of the fish tanks, and as they grow out we will once again be pushing our system density. As we have pushed the fish density in the system, we have had to keep an ever closer eye on the system chemistry. At some point, it becomes just too unstable to continue to increase the density any further.



To summarize, increasing your fish density will allow you to produce more nitrates and other nutrients for your plants. As the density increases, however, the system becomes less stable and requires more timely attention. This is true for a system of any size. As we found out, adding high pH water as a part of evaporation replacement worked well to keep the system pH in the proper range but as the fish density increased through time, the system started having new problems in the area of water chemistry. This required a greater and more timely attention and compensation in order to keep the system healthy. So, a six to ten gallon per pound ratio is a fairly safe and lay back place to be in a home aquaponics system, but if you want to get the most from the least then you can increase your fish poundage to water ratio. If you do then you will need to stay on top and ahead of your system, for it will go places it has not gone before.

Oliver

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 Post subject: Re: Fish to Water Ratios
PostPosted: Wed Mar 23, 2011 11:03 pm 
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Oliver,

If yo put 40lbs of fingerlings in a 120 gallon container. as they grow the lbs per gallon changes.

so you will need to remove fish to keep the ratio correct?

I have roughly 40 to 44 pieces of Tilapia in 40 gallons of water. All chemistry is fine and within good range only when I added additional water when I went from gravel to float beds did I experience a slight Nitrite spike but it has not hurt the fish. everything else stayed the same. After a week the Nitrite level went back down. Nitrate levels never changed ammonia levels never changed and pH is around 6.6-6.8.

So When I put the the tilapia in I put in forty Tilapia fingerlings they are growing and range in size from 3 inches to 7 at present. I am going to leave them as long as I can to see how big I can grow them in this same 40gallons of water.


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 Post subject: Re: Fish to Water Ratios
PostPosted: Wed Mar 23, 2011 11:19 pm 
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I have been eagerly anticipating this section! Thanks!


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 Post subject: Re: Fish to Water Ratios
PostPosted: Thu Mar 24, 2011 12:50 pm 
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aquaarche wrote:

If yo put 40lbs of fingerlings in a 120 gallon container. as they grow the lbs per gallon changes.

so you will need to remove fish to keep the ratio correct?

You are already at 3 gallons per pound. You will need to watch your water chemistry very carefully. If your system remains stable and you do not increase the food you are feeding your fish, then you may be able to continue without problems, but be careful. If you increase the amount of food as they grow, then you will have problems. If you don't increase the amount of food, they will stop growing at some point unless you remove some fish so the rest can use the available food to grow.

Quote:
I have roughly 40 to 44 pieces of Tilapia in 40 gallons of water. All chemistry is fine and within good range only when I added additional water when I went from gravel to float beds did I experience a slight Nitrite spike but it has not hurt the fish. everything else stayed the same. After a week the Nitrite level went back down. Nitrate levels never changed ammonia levels never changed and pH is around 6.6-6.8.

So When I put the the tilapia in I put in forty Tilapia fingerlings they are growing and range in size from 3 inches to 7 at present. I am going to leave them as long as I can to see how big I can grow them in this same 40gallons of water.

The question that comes to mind is "What are you using for a bio filter?"

If I understand what you are saying is that you have two different tanks, 40 and 120 gallons. I have given the parameters necessary for safe operation in the above article. If you deviate from these recommendations, you do so at your own risk, and that of your fish.

Continuing to add water (water exchange) will keep your fish healthy but will dilute the nutrients in your system, thereby defeating part of what you are trying to accomplish in an Aquaponics system.

I suggest you read the whole series on Aquaponics 101 to get an idea templet of what is required to make an Aquaponics system viable.

As long as you have ample dissolved oxygen and keep your pH around 7.0 then you will probably be ok. But, if you do not have enough bio-filter for the amount of food you are giving your fish, then you will have problems at the ratios you now have and will be changing as the fish grow out.

Remember, it all boils down to the amount of food you feed your fish to the amount of bio-filter you have to process the waste. This assumes that your water chemistry, including dissolved oxygen, is within an acceptable range.

As your pH drops below 6.8, the bacteria will have increasing difficulty reproducing. At around pH 6.0 you will see a rise in ammonia that can reach toxic levels. If you find this happening you will have a few choices, water exchange being one of them. Adding pH-up is another. pH up should be pure potassium hydroxide (KOH) or lime (mostly calcium hydroxide (CaOH). With lime, be careful that it doesn't contain other ingredients that are toxic to fish and plants. Dilute these chemicals with water and add slowly. Only change your pH a few tenths per day. Alternate between Potassium hydroxide and Calcium hydroxide.

I suggest pouring your diluted pH-up into the grow beds/bio-filter. It is best if you don't pour it directly into your fish tanks.

Also, if there is a way to tie the water flow between your two tanks together so there is a continual flow (only needs to exchange about once a day) then you system will be more stable and it will also reduce your workload, for you will only be making one water chemistry measurement instead of two.

Added note: In rereading this, I realized that the question about the 120 gallon tank was hypothetical. As I mentioned in the article, you need to plan ahead for your future fish density.

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 Post subject: Re: Fish to Water Ratios
PostPosted: Thu Mar 24, 2011 1:01 pm 
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This is an excellent post Oliver! I think it is right on the money! My favorite in your series thus far. :mrgreen:


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 Post subject: Re: Fish to Water Ratios
PostPosted: Thu Mar 24, 2011 1:02 pm 
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urbanfarmer wrote:
This is an excellent post Oliver! I think it is right on the money! My favorite in your series thus far. :mrgreen:


Thanks

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 Post subject: Re: Fish to Water Ratios
PostPosted: Thu Mar 24, 2011 7:23 pm 
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Oliver,

You can see what I am using for bio-filters at http://chette.tripod.com/id40.html.

They are similar to the Bio-scrubbies but are braided net with loose net wrapped inside. there is one filter pre-pump and one post pump.


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 Post subject: Re: Fish to Water Ratios
PostPosted: Thu Mar 24, 2011 11:24 pm 
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aquaarche,

I see that you have changed from gravel grow beds to a raft system I am wondering why you did that. In doing so, you have eliminated a great bio-filter, one that would process both the ammonia in the system as well as the solid fish waste. Now you have a filter of questionable value (I'm not saying that it won't work) that needs to be serviced regularly.

I am also curious as to how much aeration you have in your system, for it is very important to aerate the water in your fish tank.

From what you wrote, you changed out the bio-filter, added Tilapia, killed off some gold fish and are perhaps wondering what happened. My guess is, and it is only a guess, that you had an ammonia spike that the Tilapia contributed to but tolerated, and the gold fish couldn't handle. Again, this is speculation on my part, as I am not clear on the sequence of events based on what you wrote about on your web site.

Regardless of what you have experienced, I congratulate you on your experimentation. I believe you have, and will, learn much as you proceed with this experiment.

If there is anything I can do to help you, then please ask.

Oliver

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 Post subject: Re: Fish to Water Ratios
PostPosted: Fri Mar 25, 2011 10:09 pm 
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I will be adding 6 air stones to the grow beds 3 in each. plus I have two air stones int he fish tank so plenty of DO. Also as we know the pH goes down over a period of time because of the fish growth and food consumption. The answer here is simple. We have very hard water here with a pH between 7.2-9.0 depending on the season (rainy or dry). Adding some hard water to this system is easy.

I am not sure but I had poor growth with gravel plus after only 1 1/2 years I had to clean the gravel. with Gravel I had lower Nitrate level, low Nirite level, low ammonia but it kept the pH higher. Until we can get a grip on the gravel here I will do a float bed.

With the filters I made I have to clean the pre-filter twice a week and the post filter once a week. I have no solid waste going into the system at all. I am hoping that once we get the larger system set up. we will have a grammarus population established and even some prawns in the float beds.

My chemical levels of the current system are at the preferred levels that Susanne Friend and Tim Mann suggest for a Organic float bed system. I hope to have are operating fully organic as theirs which includes scuds, shrimp. Tilapia. When Grammarus scuds are established their shed exoskeletons it naturally add calcium to the water which counter balances the pH to 7.0.

This heterotrophic bacteria you are adding to your system. Is that naturally found in nature as a way to control food waste from the fish? or is it something like yeast which creates a bacteria that break down the solids. How does it affect your system chemistry?

At the moment my fish are doing fine and are growing (fattening) they are eating around the same amounts as before only a slight increase of food so far. They are growing. The gold fish died from territorial attacks by the Tilapia. You could see that their fins were bitten even their faces were bitten. When I had only a few Tilapia and mainly Goldies the Goldies were aggressive toward the tilapia. but once my Tilapia population increased and they out numbered the Goldies 2 to 1 that is when they became the victims. during that time the Ammonia levels as they were most of the time with gravel so low they didn't even measure in my test. So far this last three weeks the ammonia level is stable at 0.25. Nitrate at 0.70, Nitrite at 0.50, and the pH fluctuates from 6.6-7 currently today it is 6.8 because I added high pH to the water to balance it.

thanks for your articles by the way. I have found them interesting and I have cut and pasted them into Word Doc for additional reading for our ex-con trainees.

Do you like my new avatar? That is my little mermaid of 14 years. Actually she very rarely gets in the water and that pic is 19 years old now. She hasn't changed much since then. a little gain from having children but still that big beautiful smile. My youngest daughter has the same smile.


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 Post subject: Re: Fish to Water Ratios
PostPosted: Sat Mar 26, 2011 7:15 pm 
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Oliver,

I was wondering I found a filter that is full of ceramic, they look like slightly larger tube beads. Would that be ok to put inline after the pump?

As ceramic filter breaks down would it add calcium to the water?


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