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.:D
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?

[GaryD]

Hi Grassroots,

For the volume of water in your system, it's probably best to use a dilute acid solution......hydrochloric acid should be readily available in Rockhampton. Make very gradual changes and, for safety's sake, when mixing the dilute solution always add the acid to the water (and never the other way round). Add small quanties of the dilute solution and measure between doses. You need to avoid sudden pH swings - in the interests of the fish.

Shells are calcium and will (if anything) cause the pH to rise.

Normal salt is neutral so it won't impact pH. See here (http://wiki.answers.com/Q/Does_salt_affect_the_pH_of_water).

Gary

[grassroots]

Thank you for getting back to me so quickly. Yesterday I installed a couple of extra bio-filters made with clay balls, today there will be added shell grit, shadecloth, flyscreen and smallish stones for more bio-filters.
How long on average does it take for the bio-filters to affect the ammonia and nitrite?

[GaryD]

Hi Grassroots,

If your system has already cycled (and it obviously has), colonisation of a new bio-filter will occur quite quickly......since the system is already well-populated by bacteria.

Until your new bio-filters take full effect, you may have to manage persistent ammonia or nitrite levels by changing water out. Keep the water changes to just enough to keep the levels in check. Changing out too much water is just going to inhibit the colonisation of bacteria.

While the ideal ammonia and nitrite level is zero, don't be too alarmed about ammonia at 1 - 2ppm or nitrate at 0.5 if things are otherwise stable.

Lightly salting your system will mitigate against nitrite problems and lowering your pH down to 6.4 (or thereabouts) will offset any ammonia issues.

Make sure you've got plenty of aeration happening.

These are useful interim measures to adopt while you are waiting for your bio-filters to kick in.

Gary

[grassroots]

My Ammonia has dropped to .25, Nitrites are still at 1, Nitrates 5, ph has increased to 7.6 with the added shell grit. Aeration is good, I have the shell grit and clay balls above the fish tank with water sprinkling through the media, then into the tank, with a drop of about a 20cm of hundreds of little droplets of water everywhere.
Thank you

[GaryD]

Hi Grassroots,

You may have misunderstood me when referred to oyster shells. I wasn't suggesting that you add shell grit. I use oyster shells (whole ones) as bio-filter media. You were looking to lower the pH but adding shell grit (or the shell grit dust more specifically) will have the opposite effect.

The effect of the shell grit dust will be limited so you can then adjust your pH slowly downward using acid or even plain white vinegar.


Do you know where you can get oyster shells?
Look for an oyster processer in your neck of the woods. While it seems logical that the oyster shells would raise pH, the reality is that they have little effect.......but they are very good bio-filter media and they cost nothing.

Gary

[grassroots]

Nitrites are slowly dropping. I'll keep an eye out for oyster shells.