PracticalAquaponicsForEveryone2

8/14/2019 PracticalAquaponicsForEveryone2

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What Should I Feed My Fish?What Should I Feed My Fish?

The three essential elements in anyAquaponics system are fish, plants andbeneficial bacteria.

Your first task, once your fish tank is set up, isto cycle your system. The purpose of cyclingis to ensure that your system is colonised bybeneficial bacteria so that ammonia can beconverted to nitrites and then for the nitrites tobe converted to nitrates (plant food).

Once your fish tank is full, start your pump andbegin recirculating water from your tankthrough your grow beds and back to the tank.

Next, you add a source of nitrogen to the tank.

Some people use live fish to cycle theirsystems. This is a questionable practicebecause it puts the fish at risk.

I prefer Nitrogen Dosing.

A nitrogen source like fish food, cooked oruncooked prawns or pure ammonia is addedto the fish tank.

Ammonia levels will begin to rise andcolonisation of Nitrosomonas bacteria (whichare naturally present in the air and water) will

start to occur.

Bacteria numbers will increase to the pointwhere the ammonia begins to convert tonitrite. The presence of nitrite in your systemwill encourage the colonisation of a secondgroup of bacteria (known as Nitrobacter) andthese will begin the conversion of nitrites tonitrates.

After youve added the nitrogen source to thefish tank, commence daily water tests.

Once your system has registered ammoniaand nitrite readings of at least 5ppm and thenreturned to ZERO, it is cycling.

How quickly your system cycles will depend ona number of factors including watertemperature, bio-filter size, media type andwater volume. It could happen with a coupleof weeks if you take a diligent approach or itcould take considerably longer in moreadverse circumstances.

It is now time to add some fish.

Continue to closely monitor water quality untilyou confirm continuous nitrate production and,If you havent already planted out your grow

If you want to achieve optimum growth for yourfish, you should feed them a pelletised rationthat has been formulated for that particularspecies. You can buy native fish pellets fromfeed stores.

Fish pellets come in a range of sizes to suitthe size of fish you are feeding. Some pelletswill be made to float (while others will sinkquite quickly) to suit the feeding habits ofparticular species.

beds, you can do so now.

The presence of detectable levels of ammoniain your system from this point on suggests aproblem and should be addressed quickly.

Gary Donaldson

My Grow Beds and Fish TankMy Grow Beds and Fish Tankare set up.what do I do now?are set up.what do I do now?

If you would prefer a more natural diet, andyou are prepared to accept slower growthrates, you may be able to supplement yourpellets with duckweed or Azolla. You can alsofeed worms, soldier fly larvae, mealworms orother live food.

How much you feed your fish is probably ofequal importance to what you feed them.

About 3% of the total weight of fish per day isa useful guide. For example, if your fish weighabout 200 grams each, and you have 100 ofthem, you have about 20kg of fish in your tank.You would then feed 600 grams per day.

While you dont have to be too precise, if yourfish receive too little feed, theyll take longer togrow out.

If they receive too much, it will remain in thewater and will contribute to poor water quality.

Some species of fish may also develop toomuch body fat as a consequence ofoverfeeding.

Pelletised fish food comes in a variety of sizes.


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Because fish come in different sizes from tinyfingerlings to big ones, fish numbers are prettymeaningless when it comes to deciding of thecapacity of an Aquaponics system.

A much more accurate standard is kilogramsof fish per 100 litres.

The weight of fish that can be kept in anAquaponics tank will be determined by factorslike:

The size of your tank

The size of the fish The species of fish The Dissolved Oxygen levels in the water. The bio-filtration capacity of your system The level of risk that you wish to assume

Theoretically, the amount of fish that can bekept in any system is limited only its ability toconvert ammonia and nitrites to nitrates (bio-filtration) and to maintain appropriate levels ofoxygen in the water.

For practical purposes, however, the level of

risk is proportionate to the stocking rate. Whatthis means is that, if you are just managing tostay ahead of the requirement for ammonia/

You can also adjust your feeding schedule toreflect your need for nitrates. If your plants aregrowing slowly, gradually ramp up yourfeeding.

Initially, this creates more ammonia, thennitrites and eventually more nitrates. You can

then reconcile your feeding with the capacity ofyour plants to absorb the extra nutrients.

Of course, all of this assumes that your tank isat optimum temperature. If the water is colderthan optimum, you can expect that the fish willeat much less.

Its also best to spread the daily ration acrossseveral smaller feeds rather than one largeone.

Remember, uneaten food eventually becomes

ammonia. If you see food accumulating on thebottom of your fish tank, stop feeding for a dayor two. Withholding feed for a day every nowand then will probably do more good thanharm.

Gary Donaldson

nitrate removal and dissolved oxygen in thesystem, you will have very little margin forerror or mishap.

If your stocking rates are high, you will need tohave warning or back-up (preferably both)systems in place if you are to avoid injuring or

killing fish in the event of a power orequipment failure.

Conversely, if you have a very low stockingrate you may not have sufficient nitrates tofeed your plants. Aquaponics is a balancingact that must be managed effectively if usefulproductivity is to be achieved.

Gary Donaldson

How Many Fish Can IHow Many Fish Can IKeep In My Tank?Keep In My Tank?

Why I Chose Silver Perch forWhy I Chose Silver Perch for

my Aquaponic System.my Aquaponic System.The short answer is, that this species is prettytough and they are easy to get.

Many people begin by wanting to keepBarramundi in their aquaponics system.

Barramundi are well known as a good eatingfish. In that respect, Silver Perch are not evenclose in terms of their public profile.

I have dozens of visitors to see my systemevery month and very few of them have evenheard of Silver Perch.

Silver Perch are far easier to keep thanBarramundi.

Silver Perch are very tolerant of lower watertemperatures that typically occur in the wintermonths.

My Silvers are still eating well and are movingbriskly around in the tank when the watertemperature gets down to 15 deg C.

Barramundi would be starting to slow down at15 deg C and it would not be good to havethe water temperature much lower that thatfor them.

Silver Perch are not as likely to succumb tosuch diseases as white spot and fungalattack.

Silver Perch tend not to bother smaller fishco-habiting in the tank with them. I havelarge Silvers (1.5kg) and Silver fingerlings

sharing the same tank and the big fish do notbother the smaller ones.

Continued on Page 5


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Duckweed is one of the best-kept secrets ofAquaponics.

It is a high quality feedstuff that can beproduced in useful quantities at little cost andwith little effort. Of equal interest (particularlyin an Aquaponics context) is its ability toremove nutrients from water.

We began growing duckweed in 2004.Initially, we used it to supplement the

pelletised rations that we fed to our Japanesequail. In more recent times, it has become animportant part of the diet that we provide toour Jade Perch.

DuckweedDuckweedfast food for fishfast food for fishsemi-shade or somewhere that you are able toshelter them from the worst of the summerheat.

You should aim for complete and dense coverof duckweed (within the range 0.6kg/m2 1.2kg/m2) for backyard farming purposes.Much below this and algal blooms will be anissue and much above it will cause it to self-mulch. Wind or fast-flowing water will alsocause diminished production due to self-

mulching.While a variety of organic materials can beused to supply nutrients for duckweed, thelogical source for Aquaponicists is their fishtanks. Of particular importance toaquaponicists, is the plants nutritionalpreference for nitrogen in the form ofammonia.

While it is not essential, recirculating waterfrom your fish tank is desirable. Aside fromsaving you the effort of bucketing water from

your fish tank, recirculating the water willensure that the nutrient levels in yourduckweed pond remain at a consistent level.

This arrangement will also help to remove anytraces of ammonia that may be present in thetank water.

Duckweed is capable of rapid growth in watercontaining just trace elements of nutrients.Interestingly, we almost killed off a batch ofduckweed through overdosing it with poultrymanure.

Temperature and sunlight are more importantgrowth parameters than nutrientconcentrations.

Duckweed grows across a wide temperaturerange between 6oC and 33oC but wevedetermined that it grows best in a range of18oC to 24oC. We know that growth slowsprogressively up to 30oC and the plant beginsto die off quickly at around 33oC.

While it will live in pH 5 to 9, the optimum pH

for growing duckweed is in the range of pH 6.5to 7.5 also the preferred range foraquaponics systems.

Duckweed - among the smallest flowering plants inthe World - and an excellent natural food for fish.

In the right conditions, this tiny plant candouble its mass every 24 48 hours.

Its explosive growth rate enables you toharvest and feed fresh duckweed on a dailybasis.

At 35% to 40%, it has a higher protein levelthan Soya beans and higher concentrations ofthe essential amino acids, lysine andmethionine than most plant proteins.

The other great news is that growingduckweed is easy - particularly in the smallponds and tanks favoured by backyard foodproducers.

You can purchase your initial stocks from most

aquarium supply shops.

You can use any open tank, large tub or in-ground pond. Place smaller containers in


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Feeding out duckweed is as simple asdragging a kitchen sieve through theduckweed tank and placing it into your fishtank.

To avoid the duckweed from being pumpedout of the tank, we made up an inexpensive

duckweed feeder from a bucket with thebottom removed. The bucket is suspended inthe water and the duckweed is placed into thebucket. This arrangement allows the fish toaccess the duckweed without distributing itthroughout the tank.

Surplus duckweed can easily be dried andstored for later use. When drying smallquantities, we allow the duckweed to drain in akitchen sieve and then spread it thinly overseveral thicknesses of newspaper or kitchen

towel. Turn it over several times each day fortwo or three days. Store it in an airtight plasticcontainer.

Freezing is actually our preferred duckweedstorage method. We simply gather up the tinyplants in a small kitchen sieve and squeezethe excess water out of them before arrangingthe mass in a shallow plastic container.

Our first challenge was to learn how to growduckweed in consistent, predictable quantities.

Our current focus is on the full integration ofthe plant into an aquaponics system. We wantto be able to grow duckweed to removenutrients, feed fish and other small livestock

and to conserve water through reducedevaporation.

Duckweed is a must have for the backyardAquaponicist.

Bio-security Warning

Duckweed (and all other aquatic organisms inan Aquaponics system) should not be allowedto make their way back into any naturalwatercourse. Plants from an aquaponicssystem that are introduced into the wild may be

carrying disease organisms that can betransmitted to other plants, animals or fish.Cover duckweed tanks with mesh to preventbirds from drinking from the tank andtransferring the duckweed on their feathers.

Gary Donaldson

Surplus duckweed can be frozen and fed out duringcolder weather when growth may slow down.

After freezing, we turn it out of the plasticmould and place the duckweed biscuit into alarge storage container. Whenever we needduckweed for our fish, we select what we needfrom the storage container in the freezer andfloat it on the surface of the fish tank.

To summarise, duckweed is a high qualitysource of plant protein that grows quickly,

costs virtually nothing to produce and requireslittle labour. It offers the added benefit ofbeing able to remove nutrients from water.

Why I chose Silver Perch.contdThis is a useful trait for small systems. Itallows you to have Silver Perch of variousages growing out in the one tank, thusproviding a steady stream of ready-to-harvest

fish for the table.

I have just harvested a good number of mybigger fish and added 200 more fingerlings tothe same tank. In around 12 months I willhave the next crop coming along.

Silver Perch are readily available from fishhatcheries right across Australia. In mostcases, it is possible to obtain small quantitiesfor as little as one dollar per fingerling.

Silver Perch represent good value and are

easy to manage for the home hobby systemand the commercial enterprise alike.

Murray H


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How to BuildHow to Builda Grow Bed Stand.a Grow Bed Stand.

How to make a very strong and attractive growbed stand from easily obtainable materials at a

economical cost.This grow bed stand will support a standard growbed with the base at a height of 450mm aboveground.

Materials needed are:

8 standard concrete blocks 3 x 50mm x 2400mm pine/hardwood sleepers.

Tools needed are:

A square nosed shovel. Long spirit level. Hand or power saw.

Set square. Tape measure and pencil.

The cost of the materials will vary slightly from townto town. In Brisbane, at my local landscapesupplies place, the concrete blocks cost $3.50 eachand the sleepers were $15.00 each for a total tab of$73.00. Shopping around may produce a betterprice.

Confirm the location for the grow bed. You need toget this right because, once it is filled, the grow bedwill be far too heavy to move.

Getting the grow bed level is the next priority. Ithelps if you have a level piece of ground to startwith. I determined that there was about 25mm fall

from one end of the spaceto the other.

By placing one blockdown at each end andusing one of the sleeperson its edge and using thespirit level you will be ablesee if it is level.

Gradually scrape awaysmall amounts of dirtwhere required until it islevel both ways.

This phase of the construction may take some time,but be patient andspend the time toget it right.

In positioning theblocks make sureyou leave enoughroom at one end forthe drain outlet fromthe grow bed.

Once the blocks arein position and level,fill them with some

Start by scraping the dirt

back at the high end firstto get a level site.

of the same gravel that you will use in the growbed.

This helps to stabilise the blocks a little and has theeffect of helping spread the load by transferring theload over the whole footprint of the blocks.

Filling the blocks with concrete will make thestructure stronger. Depending on the nature ofyour soil, you may even decide to lay concretefootings.

Once this is finished, lay the sleepers in place.

Level ends at one end and trim the other end usingyour circular saw or hand saw to a length to suit thegrow bed.

Notice the middle sleeper has been left short toallow for the drain pipe to come out for the returnline. Now put the grow bed in place ready to load

the gravel and fit the pipe work.

How easy is that?

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