Constructing Simple RAS

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Many teachers would like to addaquatic science and/or aquacul-ture programs to their curricula.These programs add a hands-onelement that can be integrated

with math, science, and a num-ber of other disciplines (see Table1). For example, students may

learn planning, finance, market-ing and sales when studyingaquaculture as a business.Aquaculture’s relevance in histo-

ry and its potential to help feedthe earth’s ever-growing popula-tion link it to various social stud-ies. Teachers who use aquaticsystems in their classrooms findthem highly effective in translat-ing academic principles to practi-cal applications.

One of the simplest ways to initi-ate a program of this nature is tobring a recirculating aquaculture

system (RAS) into the classroom.An RAS maintains aquaticspecies while filtering andreusing the water. An RAS maybe as simple as a single smallaquarium or as complex as amulti-unit production system. AnRAS suitable for a classroom is

simple and inexpensive to build.While the greatest value of theRAS is as a teaching tool, theexperience of working with anRAS can also motivate studentsto participate and develop newlife skills. Aquaculture projectscan encourage cooperative learn-ing, bring together students of diverse backgrounds, and linkseemingly disparate skills. Someschools sell fish and plants togenerate revenue for their pro-grams. This helps students learn

sales, marketing and other entre- preneurial skills. Teachers oftenreport that students become soengrossed in working with thesystems they forget that they arestudying science and math. Thestudents take a great deal of

pride in raising fish and theylearn responsibility by working

with live animals.

VIPR

August 2005

SRAC Publication No. 450

*Auburn University, Auburn, AL

Constructing a Simple and InexpensiveRecirculating Aquaculture System (RAS)

for Classroom UseDavid Cline*

Table 1. Subjects that can be taught using a recirculating aquacul-ture system.

Biology Chemistry Physics

Math Economics Plumbing

Mechanical Systems Construction Sales

Marketing Hydraulics Language Arts

Business Planning Finance Home EconomicsFood Sanitation & Safety Nutrition Physiology

Morphology Fish Health Fish Reproduction

Genetics Art History

Sociology Carpentry Masonry

Hydroponics Computer Technology Public Relations



System components

A simple RAS system can be con-structed from items available atnearly any home improvementstore. Step-by-step instructionsfor building a system are

described and illustrated below.There are many other optionsand variations one might use, butthe system shown here has beenclassroom tested. Every RASmust include components tohold the fish, remove the solid

wastes (mechanical filter),remove the dissolved nitrogenous

wastes (biological filter), circulatethe water, maintain the tempera-ture, and aerate the water if nec-essary. Figure 1 illustrates thesecomponents and shows the path

the water will follow as it travelsthrough the system. Photo 1shows the completed system.

Fish barrel Filter barrel

Water transfer pipe 5-gallon bucketmechanical filter

Water line

Water flow

Water returnto fish barrel

Biofiltermedia

Mechanicalfilter

standpipe

FilterPads

3-inch pipewith holes

Bucketoverflow

Pump

Figure 1. A simple RAS system illustrating the components and showing the path the water follows as it travels through the system.

Photo 1. Completed system.

The first component is the culturevessel or fish barrel where thefish are housed. The water is lift-ed from the bottom of the fishbarrel (by the pump) to a plasticbucket supported by plywood onthe top of the filter barrel. In thisbucket (mechanical filter) the

water must pass through severallayers of filter material that cap-ture the uneaten feed and solidfeces. Once through the filter

pads, the water leaves the bucketby going through holes in the bot-

tom of a 3-inch pipe and then outthe stand pipe in the center of thebucket. The water then travels tothe bottom of the filter barrel andmust pass though the biofiltermedia (to remove nitrogenous

wastes) before returning to thefish barrel.

These are the tools required tobuild the system:

• PVC pipe cutter or hacksaw• Extension cord• Goggles or safety glasses• Saber saw or Sawzall®• Electric drill• Ruler or tape measure• Hole saw to cut 1 1 ⁄ 4 and 1 1 ⁄ 2 inch• Drill bits, 1 ⁄ 4-inch• Teflon® tape• Marker• Sandpaper

• Rubber gloves• Screwdriver (to match boltheads)

• Pliers or 3 ⁄ 16-inch ratchet



Table 2. Parts list for a small recirculating aquaculture system.

Materials

Quantity Size Description

2 55-gallon Plastic barrels

1 5-gallon Plastic bucket

1 2-foot x 2-foot piece 1 Ú 2-inch plywood

1 200 to 600 gallons per hour Water pump with 3 Ú 4-inch outlet

1 (optional but desirable) 2 outlets Deep-water air pump

2 1- to 2-inch Airstones

2 30 inches long Airline tubing to fit pump and airstones

Piping

Quantity Label Length Description

1 A 22 inches 1-inch pvc pipe – filter downspout

1 B 10 inches 1-inch pvc pipe – filter level control pipe

1 D 2 inches 1-inch pvc pipe – bucket overflow female to down elbow

2 E 7 inches 1-inch pvc pipe – bucket overflow downspout, water return

1 F 27 inches 3 Ú 4-inch pvc pipe – pump horizontal

1 G 35 inches 3 Ú 4-inch pvc pipe – pump vertical riser

1 H 3 inches 3 Ú 4-inch pvc pipe – pump downspout to filter

1 C 13 1 Ú 2 inches 3-inch pvc pipe – outer sleeve of filter level control pipe

Fittings

Quantity Label Size Description

4 I 1-inch Slip/threaded female – filter bottom, overflow outside, inside water returns

5 J 1-inch Slip/threaded male – one at each end of water return, filter overflow, filterbottom

1 K 1-inch 90-degree elbow – filter overflow

2 L 1-inch Tee eliminators (from Aquatic Ecosystems) to fit in 1 1 Ú 2-inch hole, or equivalent

bulkhead fittings for 1-inch pipe

1 M 3 Ú 4-inch Slip/threaded female – for pump outlet

3 N 3 Ú 4-inch 90-degree elbows – pump/water transfer fittings, water return directional

Window (optional but desirable)

Quantity Label Size Description

1 O 6-inch x 20-inch Piece of 1 Ú 4-inch Lexan®

20 P 3 Ú 16-inch x 3 Ú 4-inch Stainless steel bolts

20 Q 3 Ú 16-inch Stainless steel nuts

20 R 3 Ú 16-inch Stainless steel washers

20 S 3 Ú 16-inch Washers

2 T Tubes Plumbers Goop® contact adhesive and sealant



Instructions

1. Gather and organize necessarytools and parts.

a. Gather necessary parts and plumbing supplies. (seeTable 2).

b. Cut the pipes to the speci-

fied length using PVC-pipecutters or hack saw.

c. Label the pipes and fittings with their letter designations.

2. Prepare barrels.

a. Obtain barrels, preferablyfrom a food or drink proces-sor/bottler, and rinse themthoroughly. You may alsouse soap barrels from a car-

wash. Do not use chemicalbarrels as there may beresidue that could be toxic

to the fish and/or humansconsuming the fish.

b. Using a saber saw orSawzall®, cut the top fromone barrel (filter barrel), leav-ing a 1- to 2-inch rim aroundthe top edge. The rim helpsmaintain rigidity. (Photo 2b)

Photo 2f.

b. Using your traced circle asa guide, cut 1 ⁄ 4 inch inside

the line using your sabersaw. Gently remove burrsand smooth very lightly

with sandpaper. This willensure that the lower partof your bucket fits snuglyinside the hole while allow-ing it to be supported bythe structural ring on thebucket. You can alwaysmake the hole larger, but itis difficult to make it small-er. (Photo 3b)

d. Using a 1 1 ⁄ 4-inch hole saw(this is an attachment for anelectric drill), cut a hole 1inch back from the centerof the remaining half of thebarrel top (fish barrel). This

will help hold the pipingthat goes from the pump inthe bottom of the fish barrel

to the filter barrel. (Photo2c)

e. Smooth rough cut edges with sandpaper to removeburrs and sharp edges.

f. Using a 1 1 ⁄ 2-inch hole saw,cut one hole in each barrel30 inches from the floor.Gently remove burrs andsmooth very lightly withsandpaper. These holes arefor the water return fromthe filter barrel to the fish

barrel. (Photo 2f) Note: If you use traditional bulkhead fittings be sure to check for the appropriate hole size.

Photo 2g.

c. Cut one-half of the top outof the other barrel (fish bar-rel), leaving a 1 - to 2-inch

rim around the opening.(Photo 2c)

Photo 3a.

Photo 3b.

3. Filter barrel assembly

a. Place the 5-gallon bucketupside down in the centerof the 2-foot x 2-foot pieceof plywood and tracearound the opening of thebucket. This will be yourguide for cutting the hole inthe plywood. (Photo 3a)

g. Insert the tee eliminators(L) into the holes. The holesneed to be as uniform andsmooth as possible to allowthe tee eliminators to sealthem properly. (Photo 2g)

Photo 2b.

Photo 2c.



d. Cut another 11

⁄ 4-inch holein the side of the 5-gallonbucket between the structur-al rim and the top of thebucket about 2 inches fromthe top. Gently removeburrs and smooth very light-ly with sandpaper. This hole

will be the overflow into thefilter barrel in case themechanical filter gets

plugged. (Photo 3d)

g. Slip the 22-inch piece of 1-inch pipe (A) into themale/slip fitting on the bot-tom of the bucket. This

pipe will direct water fromthe mechanical filter to the

bottom of the biological fil-ter. (Photo 3g)

Photo 3c.

Photo 3g.

Photo 3d.

Photo 3e.

e. Fit a 1-inch male/slip fitting(J) through the hole in thebottom of the bucket andsecure it on the inside witha 1-inch female/slip fitting(I). This joint does not haveto be watertight becauseany leaks will fall into thefilter barrel. (Photo 3e)

Photo 3f.

f. Repeat this procedure for thehole on the side of the bucket.This joint, however, should beas watertight as possible to

prevent water from leakingbetween the fitting and thebucket. (Photo 3f)

Photo 3h.

h. Slip the 10-inch piece of 1-inch pipe (B) into thefemale/slip fitting on theinside bottom of the bucketThis will be the overflowfrom the mechanical filterinto the biological filter portion of the barrel. (Photo3h)

Photo 3i.

c. Using the hole saw, cut a1 1 ⁄ 4-inch circular hole in thecenter of the bottom of the 5-gallon bucket. Gentlyremove burrs and smoothvery lightly with sandpaper.This bucket will serve as themechanical filter and willdirect water to the biological

filter below. (Photo 3c)

i. Using the 13 1 ⁄ 2-inch pieceof 3-inch pipe (C). Draw aline around the pipe 3 inch-es from one end. Holdingthe pipe securely, drill anumber of randomly spaced1 ⁄ 4-inch holes in it betweenthe line and the end of the

pipe. (Photo 3i)



6. Attaching the pump

a. Purchase or locate a pump with a 200- to 600-gallon- per-hour flow rate. The fol-lowing steps will vary depending on the pump selected.

b. If you have a pump with a3 ⁄ 4-inch threaded outlet, youcan attach a female/slip fit-ting to the pump and slipthe 35-inch piece of 3 ⁄ 4-inch

pipe (G) into the other side.

c. If you have a pump with a3 ⁄ 4-inch non-threaded outlet

you can wrap Teflon® tapearound the pump outletuntil it is thick enough toslip inside the 3 ⁄ 4-inch riser

pipe. You may also wish toattach a 90-degree elbow tothe inlet of the pump overthe inlet screen and direct iat a 45-degree angle to thebottom (optional). This willhelp pick up wastes anddebris from the bottom of the tank.

f. Cut a 1 1 ⁄ 2-inch hole in the plywood using the traced cir-cle from the elbow as aguide.

g. Slip a 7-inch piece of 1-inch pipe (E) into the elbow, with the other end droppingthrough the hole in the ply-

wood. (Photo 4g) Photo 5c.

5. Pump-to-filter assembly

a. Place a 3 ⁄ 4-inch, 90-degreeelbow (N) on each end of the 27-inch piece of 3 ⁄ 4-inch

pipe (F) and turn them sothey are facing the samedirection.

b. Slip the 35-inch piece of 3 ⁄ 4-inch pipe (G) into one of the 90-degree elbows andthe 3-inch piece of 3 ⁄ 4-inch

pipe (H) into the other 90-degree elbow.

c. Place the 35-inch piece of 3 ⁄ 4-inch pipe through thehole in the uncut half of thetop of the filter barrel.(Photo 5c)

j. Place the 3-inch pipe, holestoward the bottom, insidethe bucket over the top of the 1-inch center pipe. Thisouter pipe forces the waterto travel through themechanical filter media to

the bottom of the bucketbefore overflowing into thebarrel below. (Photo 3j)

4. Mechanical filter emergencyoverflow assembly

a. Place the 2-foot by 2-footboard over the top of thefilter barrel.

b. Place the bucket into thehole in the plywood. Itshould rest securely on thestructural rim of the bucket.

If the hole in the plywoodis too snug, trim the hole asnecessary.

c. Fit the 2-inch piece of 1-inch pipe (D) into the male/slipfitting on the outside of thebucket. Push it in as far as

possible.

d. Place a 1-inch, 90-degreeelbow (K) on the other endof this 2-inch piece andsecure it with the openingof the elbow directed at the

plywood. (Photo 4d)

Photo 4d.

Photo 4e.

Photo 4g.

e. Using the outer edge of theelbow fitting as a guide,trace a circle onto the ply-

wood. Make sure the down- ward facing elbow on the plywood is situated so as toallow the attached down-

spout to fit easily inside therim of the barrel. (Photo 4e)

Photo 3j.



e. Hold the Lexan® windowfirmly to the barrel, takingcare to line it up.

f. Drill the holes at the corners(1 ⁄ 2 inch from each corner),first securing them withbolts as you go. (Photo 7f)

Photo 7a.

Photo 7b.

Photo 7c.

d. If your pump has a 1 ⁄ 2-inchoutlet you will need abushing/reducer fitting that

will reduce the 3 ⁄ 4-inch riser pipe to match the pumpoutlet.

e. If you use a pump with a

capacity greater than 500gallons per hour, you may

wish to insert a ball valvein the middle of pipe (F) tocontrol the water flow tothe mechanical filter.

7. Window installation (optional,but desirable for viewing fish)

a. Place the 6-inch x 20-inch piece of Lexan® near thecenter of the barrel. Lexan®is more flexible thanPlexiglas® and is less likely

to crack or break duringinstallation. Using a mark-er, trace the outline ontothe side of the barrel. Havesomeone else hold theLexan® flat to the curvedbarrel. (Photo 7a)

Photo 7d.

Photo 7f.

Photo 7g.

c. Cut out the inner rectangleusing the saber saw. (Photo7c)

Photo 7i.

b. To mark the area to be cutout, measure and make amark 1 inch in from each of the corners along the sides.Connect these marks with a

straight edge to create aninner rectangle that is 1 inchsmaller on all sides than theoriginal outline. This leaves a1-inch overlap to attach andseal the window. (Photo 7b)

d. Smooth any rough edges with sandpaper. (Photo 7d)

g. Drill seven holes across thetop (2 3 ⁄ 4 inches apart) andthree holes down each side (21 ⁄ 2 inches apart). (Photo 7g)

h. Remove the window and put on rubber gloves.

i. Apply Plumber’s Goop® lib-erally around the edge of the opening. (Photo 7i)



j. Put plenty over the top of the drilled holes. It will takemore than half the tube.Work quickly.

k. Replace the window andline up the holes. Place adrop of Goop® over each

hole. Working from one endto the other, place a regular

washer on the bolt andthread it through the hole.Secure a stainless steel

washer and nut to each bolton the inside of the barrel.Work quickly to thread andsecure bolts before Goop®gets too stiff. (Photo 7k)

b. Make sure not to cross thethreads and secure as tight-ly as possible. You may

want to lubricate thethreads with water.

c. Place the barrels closetogether and fit the remain-

ing 7-inch piece of 1-inch pipe (E) into each of themale/slip fittings. (Photo 8c)

traditional bulkhead fittingsare in place, the 90-degreeelbow should slide into thefemale fitting.)

9. Finishing up (Photo 9)

a. Move the barrels to theirfinal location. Locating thebarrels near a drain or sinkmakes it easier to add orremove water.

b. You may wish to considergluing the pvc pipe joints of the pump-to-filter assembly.This is the only pipingunder pressure that couldcome apart. The other fit-tings should be tight enoughthat they don’t leak. If youdo find a leak, you can goback and wrap the screw fit

tings with Teflon® tape, gluethe pipes together, or use theremaining Plumber’s Goop®as a patch.

c. Fill the fish barrel with water to a few inches belowthe filter return pipe andcheck for leaks around the

window.

d. Put a few gallons of waterin the filter barrel andadjust the distance between

Photo 9.

l. Allow Goop® to cure for 24hours before adding any

water to the barrels.8. Connecting the barrels

a. Thread one of the 1-inchmale/slip fittings (J) intoeach of the tee eliminators.(Photo 8a)

Photo 7k.

Photo 8a.

Photo 8c.

d. Thread one of the 1-inch maleslip fittings (J) into the teeeliminator on the inside of the fish barrel. Fit a 3 ⁄ 4-inch,90-degree elbow (N) into theslip end of the 1-inch male fit-ing to direct the returning

water in a counterclockwisecircular flow pattern. (Note: If



the barrels, making sure theconnecting pipe fits snuglybetween the barrels. Thebarrels are very difficult tomove once full, so makesure to put them where you

want them to stay. Note:

The full barrels may weighmore than 800 pounds, somake sure there is adequatestructural support.

e. Plug in the pump (in a GFI- protected plug), circulate the water, and check for andrepair any leaks.

Breaking in the system

As with any aquarium or otherRAS, there is break-in period. Ittakes approximately 45 days for

a biofilter to colonize with theappropriate bacteria (Nitro-somonas and Nitrobacter ) to breakdown fish wastes. This break-in

phase can be helped along by theaddition of a few fish to the sys-tem. Their waste will providethe food the bacteria need to getestablished. After the filter is

populated with the bacteria, addmore fish to the system.

The carrying capacity of the sys-tem is generally determined bythe filter’s ability to remove

solids and break down the fish waste, a process called the nitri-fication cycle. It is described ingreater detail in SRAC publica-tion 454, “RecirculatingAquaculture Tank ProductionSystems: Management of Recirculating Systems.” Simply

put, if you do a good job of removing the solids from the sys-tem with the mechanical filter,the amount of surface area pre-sent in the biofilter will deter-mine how much bacteria you can

grow, how much you can feedthe fish, and, thus, how many

pounds of fish the system canhold. A general rule of thumb isthat it takes at least 5 square feet

of biomedia to handle 1 poundof fish being fed at 2 percent of body weight per day.

Selecting mechanicaland biofilter media

The media for this system werenot specified so that individualscould experiment with differentmedia and see what works bestfor them. Inexpensive possibili-ties for mechanical filter mediainclude sponges; pillow filling(spun nylon), available in craftstores; floor scrubbing and pol-ishing pads (with no soap or pol-ish residue); or a commercialfiber mat material. Look for anontoxic material that will allow

water to pass though while

retaining solids. Also look formaterials that can be easilycleaned.

There are a number of possibili-ties for biofilter material as well.Nontoxic material with a highsurface area-to-volume ratio is agood place to start. Finding thesematerials and calculating the sur-face area is a great activity forstudents. Aquaculture supplyhouses have many materials, but

you may be able to find some-thing locally as well. Examples

of creative biofilter materialsinclude cut-up soda straws, PVC

pipe rings or shavings from alathe, plastic forks, plastic eggcartons, Styrofoam® packing

peanuts (remember they float),etc.

Using 1 cubic foot of commercialbiofill (similar to long pvc pipeshavings) that has 250 squarefeet of surface area per cubicfoot, the system could theoreti-cally hold 50 pounds of fish.

Using the same volume of 1-inchbioballs with 160 square feet of surface area per cubic foot, thesystem could theoretically hold32 pounds of fish. These com-

mercial biomedia materials arerelatively expensive ($30 to $60

per cubic foot). However, you would have to cut up 322 feet of 1-inch pvc pipe into 1-inchlengths to get the same amountof surface area as 1 cubic foot of

biofill material. The cost of the pvc pipe and the effort to cut itup brings the cost of the manu-factured material into perspec-tive.

These fish capacity calculationsassume that all other water quality parameters are kept at opti-mum levels. Holding or growing50 pounds of fish in this system

would require the addition of pure oxygen and a variety of other management strategiesbeyond the scope of this publica-

tion. In reality, under typicalclassroom conditions, this systemcan be expected to hold 8 to 12

pounds of hardy fish such astilapia or koi carp. For moreinformation on tank productionof tilapia, see SRAC publications282 and 283. For more informa-tion on koi and goldfish, seeSRAC publication 7201. If youselect a species that requires tem

peratures outside the range of normal room temperature, you

will have to heat or cool the water as necessary. Adding theoptional deep-water air pump

with an airstone in each tank wilenhance the system’s perfor-mance by helping to supply oxy-gen to the fish and to the bacteriain the biofilter.

System maintenance

General system maintenanceincludes keeping track of the

water quality and quantity, feed-ing the fish, and cleaning the

mechanical filter as necessary. If one or more water quality para-meters moves outside acceptablelevels, the easiest solution is to



exchange some of the water. Toavoid problems, you might con-sider changing about 10 percentof the water each week. If yourreplacement water contains chlo-rine, it will be necessary to add achlorine remover to protect the

fish and the bacteria on the filter.

Classroom activities

Teachers have used the followingactivities to demonstrate real-

world applications of the mathand science principles taught inthe classroom.

• Determining the volume of fish culture vessels

• Calculating feeding rates andfeed conversion ratios (FCR)

• Calculating fish growth rates

• Calculating water flow andexchange rates• Converting English units to

metric units• Determining the surface area

of filter media and culturetanks

• Testing the water and analyz-ing its chemistry

• Developing graphs from col-lected data

• Examining the internal andexternal anatomy of fish

A similar list of activities couldbe developed for each of the dis-ciplines listed in Table 1. The

possibilities are limited only bythe knowledge and creativity of the teacher and students.

ConclusionA wealth of anecdotal evidencesuggests that RAS systems andactivities provide exciting oppor-tunities for learning. Teachers

who use these systems claim thata number of other valuable,nonacademic lessons are learnedas well. They say these systems:

• Motivate marginal students to participate and develop lifeskills that will enable them tocontinue their education

and/or become productivemembers of the workforce.• Give students a sense of

responsibility and help themlearn the rewards and conse-quences of that responsibility.

For more information on buildingand using an RAS for classroominstruction, visitwww.ag.auburn.edu/ras.

Suggested readings

SRAC 282, “Tank Culture of Tilapia

SRAC 283, “Tilapia: Life Historyand Biology”

SRAC 451, “Overview of CriticalConsiderations”

SRAC 452, “Management of Recirculating Systems”

SRAC 453, “A Review of Component Options”

SRAC 454, “Integrating Fish andPlant Culture”

SRAC 7201, “Species Profile: Koiand Goldfish”

Soares, S. J., J. K. Buttner andDale F. Leavitt. 2001.Aquaculture CurriculaResource Guide: A Resource

Tool for the Aquacul-tureEducator. MassachusettsDeparment of Food andAgriculture, MA. 59 pp.

Special thanks to Hugh Hammer,Tim Adams and Jim Brooks at theGadsden State Community CollegeAquaculture Education andDevelopment Center, and to J. J.Newman of the New HampshireCooperative Extension Service, fortheir help with the system design,

assembly and photographs.



The work reported in this publication was supported in part by the Southern Regional Aquaculture Centerthrough Grant No. 2003-38500-12997 from the United States Department of Agriculture, Cooperative StateResearch, Education, and Extension Service.

SRAC fact sheets are reviewed annually by the Publications, Videos and Computer Software SteeringCommittee. Fact sheets are revised as new knowledge becomes available. Fact sheets that have notbeen revised are considered to reflect the current state of knowledge.

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Constructing Simple RAS