Grassroots system

[grassroots]

I'm now ready to start my first Aquaponics set up. My fish tank can hold 1200litres, up to 2000litres.
The plan is to have 1200litres in the fish tank, which runs into a duckweed tank, then than back into the fish tank on a continuous flow system. It will be stocked with Jade or Silver Perch. I am using wicking beds to grow vegetables, so I am more interested in raising fish in this set up, feeding them bsf and duckweed as well as pellets as a backup. I am in the Central Queensland area. The options for the size of the grow beds and duck weed tank are 1@155litre, 1@211litre and 3@570litres.
Will this work?
Can I just have a duck weed tank, or is there a need for the grow beds to convert the amonia into usable nitrate?
What size grow bed and duckweed tank would be best?
How many fish should I start with?
Where can I buy fish pellets?
Is there anything else I am missing?

Thanks in advance

[GaryD]

Hi grassroots,

I'm now ready to start my first Aquaponics set up. My fish tank can hold 1200litres, up to 2000litres.
The plan is to have 1200litres in the fish tank, which runs into a duckweed tank, then than back into the fish tank on a continuous flow system. It will be stocked with Jade or Silver Perch. I am using wicking beds to grow vegetables, so I am more interested in raising fish in this set up, feeding them bsf and duckweed as well as pellets as a backup. I am in the Central Queensland area. The options for the size of the grow beds and duck weed tank are 1@155litre, 1@211litre and 3@570litres.
Will this work?

Can I just have a duck weed tank, or is there a need for the grow beds to convert the amonia into usable nitrate?

For the size of duckweed tank that you're likely to have, I'd suggest that you either add media-based grow beds or incorporate a trickling bio-filter into your design. A bio-filter would be excellent when used in conjunction with your wicking beds. I'd set your duckweed tank up so that the water flows through that immediately after coming out of your fish tank. That way, it will function as a sedimentation tank as well as growing your duckweed......and you can vacuum the bottom weekly as you harvest your duckweed. The sediment that you suck off the bottom of your duckweed tank will go down very well on your wicking beds.

How many fish should I start with?

Your tank will support 50 fingerlings comfortably......and, for your climate, I'd go with Jade Perch - they're an easy one year grow out and they're very hardy......and they eat duckweed.

Where can I buy fish pellets?

I buy mine from Grobest at Beenleigh.

Gary

[grassroots]

Thanks Gary for the information, I have been reading with interest your new setup. What are you using for your biofilter and how are you going to make it?

[grassroots]

I just found this website on duckweed www.p2pays.org/ref/09/08875/fig23b.gif

[GaryD]

Hi,

I'll probably use a rectangular section fibreglass tank and fill it with oyster shells.

During the past few weeks, I've been running such a bio-filter on an auto-syphon - it works a treat and it ensures that the oyster shell media is wet evenly.

Gary

[grassroots]

http://www.p2pays.org/ref/09/08875.htm Sorry about the last post, I think that this is the correct one.

[grassroots]

I now have 50 Jade perch in a tank that holds over 2000 litres, 150 Silver perch in 1000 litre tank and 100 Silver perch in a 1000 litre tank. All up I have 6000 litres in my system including a 2000 litre sump come floating grow bed, they are all joined together making it one large system.
My Ammonia levels are .5 ppm, Nitrite 1 ppm, Nitrate 5 ppm and Ph is 7.4.
What are the best levels for Ammonia, Nitrite, Nitrate and Ph?
Is there anything I need to look at changing in the system?

[GaryD]

Hi Grassroots,

I think you need some more bio-filtration (or more grow beds) to handle the waste produced by your system. Your most cost effective option is to set up a trickling bio-filter (or two) made from plastic barrels and filled with oyster shells.

I'd prefer to see lower ammonia and nitrite levels. While both of your species are relatively hardy, your current levels don't give you much latitude, so I think it would be wise to work toward getting both ammonia and nitrites back closer to zero.

I'd also suggest that you salt your tanks at the rate of 1kg per 1000 litres......to mitigate against nitrite toxicity. If you slowly bring your pH down to around 6.4, you'll reduce the overall toxicity of any ammonia spike.......and your plants will be able to access the nutrients in your system more effectively.

Gary

[grassroots]

Thank you for the advice, I plan to make some more bio-filters tomorrow.
I have read that the ideal rates for Ammonia and Nitrite is .25 is this accurate?
Also that nitrates can be as high as 10ppm - 1000pm, this seems very high.
Will that amount of salt hurt the plants?
Do you know where you can get oyster shells?

[grassroots]

Which is the best way to reduce the ph.
I've read that lime, lemon and or pineapple peelings soaked in the system will lower the ph, vinegar is supposed to lower it as well.
Won't shells lower ph?
If I add salt won't that raise the ph?