Amount of fish in my beginners' system

[Louise]

I'll be starting up my first aquaponic system this spring. I have 10 tilapia currently in an ordinary aquarium indoors. They are 10-15 cm now (4-6 inches). My planned AP system will have a 300 litres fish tank (66 gallons), and a grow bed that is approximately 2 metres x 60 cm x 27 cm. That adds up to 300 litres of media, so, the same as water volume in the fish tank.

I checked the measurements against the "rules of thumb" here, and they seem to be ok.

But how many fish would you recommend in that volume? I have one recommendation from a swedish aquapon who is more used to cold water fish, and he suggests 6-8 fish in that, but I have seen much larger amounts suggested.

What would you suggest? Do I need to buy more tilapia, or will it be ok with the 10 I have?

If 10 fish do not provide enough fertilizer, would it be an option to top it up with pee, until my fish have multiplied themselves? It isn't all that easy to get hold of tilapia in Sweden.

Louise

[Louise]

Oh, and two more questions on fish:

In the recommendations, where it expresses a sum of weight of fish - does that mean the finished fully grown weight, or the current weight? I have Mozambique tilapia (as nile tilapia wasn't available) - what is their final weight?

Also - what type of aerator of the water is needed, apart from the circulating of water to the grow beds?

[TCLynx]

Hi Louise,

     I think your 10 tilapia will be plenty for your little starter system.  Perhaps you can use squeezings from the current aquarium filter to help jump start your media bed.  And if the Tilapia are currently comfortable in their aquarium you might think about cycling up the bio-filter for your AP system fishless by adding some for of ammonia (or pee) to it before you put the fish in so that you can get some nitrates converted ahead of time without risking stressing the fish. 

I do not recommend adding any ammonia source like pee or other fertilizers to a system to up the nitrates while there are fish in the system unless you are expert and can handle the consequences if you overdo it and cause spikes and perhaps kill your fish.

The recommendations that you have seen probably are dealing with weight total in a system at any given time but those numbers usually are not all that useful to a home/backyard aquaponics system since how many people are going to go to the effort of weighing their fish all the time?  Also the higher numbers are generally the MAX numbers a given amount of tank or grow bed might handle and are also not very appropriate to a brand new system being operated by people new to aquaponics.

Better numbers might be something like, stock say 20 fish per 500 liters of grow bed.

Now keeping in mind that your system is very small so swings can happen fast.  I would say 10 fish in a 300 liter fish tank with a 300 liter media filled grow bed should be plenty.  Especially if the water level in the fish tank fluctuates when the grow bed floods and drains.

If you find your fish are having trouble providing enough nutrients for the plants, you might improve on the feed and make sure the water is warm enough for tilapia to eat well.  However, for an indoor system with only a single grow bed that size, you are more likely to have plenty of nutrients unless you have really good lighting for the plants and are very good at keeping the bed fully planted.

A bit of seaweed extract while the system is new can sometimes help the plants get a good start until it matures and can convert the fish waste solids into the plant usable trace elements.

[Louise]

Thank you! This sounds hopeful!

My system will be in a greenhouse when I set it up, so I will have ok light. But since I'm in a cool climate, I will always need to bring my tilapia indoors in winter.

Any ideas on the need of aeration?

[TCLynx]

For aeration.  Well if your pump runs constantly and has extra flow to spray back into the fish tank all the time, then you might not need extra aeration for tilapia.

However, if you want to know for an air pump.  I would say look for an air pump that can deliver perhaps 6 liters per minute at around 13 kpa??  I don't even know what size ranges the little air pumps tend to come in (and forgive me I am converting from imperial measure to metric to come up with these figures.)

Beware water temperature fluctuations in such a small system out in a greenhouse.  Temperature swings that are too extreme from day to night to day can be really hard on fish and tilapia like warm water, they won't eat well if the water is too chilly for them.

[Louise]

I was planning to run my pump for the grow bed on a timer. So the fish need another pump for aeration. Either I could use what I'm using indoors now: just a filtering pump that circulates the water enough to get it aerated. Or I could buy one of those air pumps that make bubbles (though I read somewhere that they are pretty useless). Or, in fact, I have a little pump intended to make a mini fountain in an ornamental pond. I guess that would do just fine, wouldn't it?

When it comes to temperature, I don't know exactly what to expect in the greenhouse. Swedish summers can vary quite a lot, from rainy and chilly 10-18 degrees Celcius (50-65 F), or it could be 18 - 30 C (65-85 F). In the greenhouse it could get up to 40 C (104 F). To eaven out the swings, I'm planning to have the fish tank partly dug into the ground. In case that gets too cold, mainly in the beginning of the summer, I plan to use my ordinary fish tank heater. But what I'm pondering is whether to put the aquarium in an insulating box of polystyrene. I have some 10 cm (4 inch) thick pieces of polystyrene laying about too. (As you might have figured out by now, I'm a collector of "things that might come in handy".)

TCLynx said:

For aeration.  Well if your pump runs constantly and has extra flow to spray back into the fish tank all the time, then you might not need extra aeration for tilapia.

However, if you want to know for an air pump.  I would say look for an air pump that can deliver perhaps 6 liters per minute at around 13 kpa??  I don't even know what size ranges the little air pumps tend to come in (and forgive me I am converting from imperial measure to metric to come up with these figures.)

Beware water temperature fluctuations in such a small system out in a greenhouse.  Temperature swings that are too extreme from day to night to day can be really hard on fish and tilapia like warm water, they won't eat well if the water is too chilly for them.

[Patti Taylor]

Definitely get an air pump for back up purposes... if the water pump ever goes bad your fish will still have air and survive.I keep another air pump on a inverter with battery backup just in case of a power outage.

[Louise]

Great tip, thanks!

[TCLynx]

Air pumps for aeration and circulation are actually quite effective as long as you get one big enough for the purpose.  Bubbles cause bottom water to rise to the surface and it is this mixing that actually causes more aeration to the fish tank water than the actual bubble contact with water.  But it is important to size your air pump property since a little 2 watt air pump meant for a 40 liter aquarium is not going to be effective at pumping air down into the bottom of say an IBC fish tank.

Small fountain or power head type water pumps for aeration might work but you have to make very sure you keep them from getting clogged up since they become totally useless for aeration if they are clogged and not flowing properly.  While water pumps can be very effective for aeration, the fact that they are far more prone to clogging than air pumps mean they are not foolproof backup (then of course most anything we try to make foolproof, fate usually makes a better fool if you know what I mean. )

As for digging the tank into the ground.  In a northern/ cold winter climate, the ground is not going to be an appropriate insulator for Tilapia (it will just keep the water from warming up in the spring which won't be good for tilapia.)  I would recommend insulating the fish tank even if you do put it in the ground in a cold climate situation.  Find out what your average ground temperatures are and only use ground coupling if those temperatures are appropriate for the fish you intend to raise other wise you will be wasting money warming the ground with your fish tank heaters in the spring.  If you were growing trout, it would be a different story and the ground coupling by digging the fish tank in might be a good idea and opening up the greenhouse during summer would be necessary so you didn't warm the water too much.  But for Tilapia, They can handle very warm water and warming your water enough in the spring/fall will be the biggest challenge for you.

[Vlad Jovanovic]

Alex...You seem to be pretty knowledgeable in many things electric...When over-sizing inverters for (smallish 150Watt) pumps what, in your opinion, is is the ROI limit? 2x's? 4x's? I understand that in this case 'bigger is better'  (inverter) but at what point does it become 'uselessly big,' in terms of how much your paying? Generally speaking of course. 

Oh yeah, mono-phase, European 220volt...if it makes a realistic difference...

alex batista said:

Definitely get an air pump for back up purposes... if the water pump ever goes bad your fish will still have air and survive.I keep another air pump on a inverter with battery backup just in case of a power outage.

[Patti Taylor]

Truthfully I dont know much on Europen voltages Vlad and how that will effect efficiency.My buddies in the Solar industry have always recommended 50% of your watts minimum to account for fluctuations (225w) in the US.I believe in colder climates you may want to stick with a pure sine wave(reliable more expensive) but if temperature isn't an issue then you can save some money with a modified.I tend to re-purpose many thing I find in garage sales or craigslist, so my 800 w I found for 5 buck may be overkill but if I need to expand I wont have to go out and buy a bigger one.

[Bob Vento]

Sorry to chime in here, but I am confused,  I understood that the returning water into the fish tank from the grow bed above  was adding enough aeration as it splashed into the tank? Does one need to add additional aeration?

Regards,

Bob

Louise said:

I was planning to run my pump for the grow bed on a timer. So the fish need another pump for aeration. Either I could use what I'm using indoors now: just a filtering pump that circulates the water enough to get it aerated. Or I could buy one of those air pumps that make bubbles (though I read somewhere that they are pretty useless). Or, in fact, I have a little pump intended to make a mini fountain in an ornamental pond. I guess that would do just fine, wouldn't it?

When it comes to temperature, I don't know exactly what to expect in the greenhouse. Swedish summers can vary quite a lot, from rainy and chilly 10-18 degrees Celcius (50-65 F), or it could be 18 - 30 C (65-85 F). In the greenhouse it could get up to 40 C (104 F). To eaven out the swings, I'm planning to have the fish tank partly dug into the ground. In case that gets too cold, mainly in the beginning of the summer, I plan to use my ordinary fish tank heater. But what I'm pondering is whether to put the aquarium in an insulating box of polystyrene. I have some 10 cm (4 inch) thick pieces of polystyrene laying about too. (As you might have figured out by now, I'm a collector of "things that might come in handy".)

TCLynx said:

For aeration.  Well if your pump runs constantly and has extra flow to spray back into the fish tank all the time, then you might not need extra aeration for tilapia.

However, if you want to know for an air pump.  I would say look for an air pump that can deliver perhaps 6 liters per minute at around 13 kpa??  I don't even know what size ranges the little air pumps tend to come in (and forgive me I am converting from imperial measure to metric to come up with these figures.)

Beware water temperature fluctuations in such a small system out in a greenhouse.  Temperature swings that are too extreme from day to night to day can be really hard on fish and tilapia like warm water, they won't eat well if the water is too chilly for them.

[Louise]

The way I understand Alex tip, is that it's good to have an alternative in case of a power cut, which seems like a very good idea. But apart from that, I have seen several tips on having an extra hose circulating water back to the fish for aeration. A swedish aquapon I talked to grows trout and other fish that are very dependent on well oxygenated water, and he uses some kind of aerator he calls a "pillar aerator" (my own translation from his swedish expression). You can see it here: rainbowfish.se

Different fish have different requirements on the oxygen in the water.

But here are loads of experts in this forum that can give more full answers!