Backyard Aquaponics
A place to discuss aquaponics

I'm setting up a small experiment this year for a uni dissertation project comparing growth rates of lettuce in aquaponic vs. straight hydroponic systems (I'm a hort. student so concentrating on plants not fish).

I'm looking to run a continuous flow/expanded clay aggregate/goldfish system with the growing media in rainwater gutters. The tanks will be about 80l and I'm looking to grow 10-15 lettuce plants in each system. I'm thinking about 4 or 5 (probably 100mm body length) goldfish in each tank.

Any thoughts/potential problems?

Cheers,

Neal

Hmmmmm

Hi Neal

How are you going to make the nutrient component of the hydroponic system "compatible" with that of fish waste? If you use a very concentrated hydroponic solution your hydroponic plants will fall over, if too dilute.. the plants won't get a good growth rate .

Are the numbers of fish you propose going to give adequate and comparable (in relation to the hydroponic system) conentrations of nitrogen for protein development.

I think you have some reading to do and maybe have to "fine tune" your experiment. - contol variables etc. etc. (I would hate to be a student again!)

Also please think about this.

Will the results be useful? Uni supervisors really do like something that can be applied later to Masters or PhD research or something that will be useful to industry or in this case maybe food aid.

May I suggest that you look at some papers done by Masters or PhD students on the lines that you are thinking of, and then look for a question that they raise, and then maybe see if you can develop a real "tight" question that you can do your experiments on.

Hope this helps.

Johnnie

Hi Neal,

If you're doing a side-by-side comparison of the two systems and focusing on on growth-rates then i would strongly suggest that you have the aquaponics system "cycled" before you begin the study.

I've read many comparisons like the one you are suggesting where the results show the aquaponics plants yellowing and stunting within a week of germination. I believe this to be because the aquaponics system had not "cycled" and hence no nitrates were being produced to sustain the plants. Cycling may take over a month in some cases. Browse the forum, there are posts covering cycling.

The fastest cycling will be had at between 25C and 30C try and keep the PH at 7.5 and "seed" your grow bed with gravel from the first 10cms of a well established aquarium and also "slime" from a well established aquarium filter. Try and deposit both of these in the bottom to middle layers of your new grow bed media so they are kept dark and moist (they will ot tolerate ANY drying).

If you want to be CERTAIN of the state or progression of your cycling then use test kits. Your system is FULLY cycled when both your AMMONIA and NITRITES are 0.0PPM. No need to test for NITRATES.

Be aware that ammonia will peak and then begin to taper down. Nitrites will start when the ammonia begins to drop. Ammonia will reach 0 ppm while nitrates are still high, cycling will be complete when nitrites have dropped.

I ususally wouldn't go to this much trouble / detail, but i strongly feel that many aqua VS hydro tests are corrupted due to this fact.

be sure to read http://www.bioconlabs.com/nitribactfacts.html

Keep us posted

Steve

Neal,

I had a re-think, you may as well measure nitrates as it will give you raw data that you could probably compare to the hydroponics solution analysis

Also, how many lettuce plants were you going to supply with water from your 80lt fish tank?
steve

Thanks guys, that was quick!

You've basically said all the stuff I was thinking.

As it's only a short project (4-5 months) rather than a 'real' piece of research, I'm trying to keep it as simple as possible. I'm trying to approach the project from a water conservation, waste reduction, fuel economy perspective. Also as a possibility for grower diversification e.g. tilapia in glasshouses alongside lettuce.

I'll be running the 'control' with a nutrient solution made to the same concs as a commercial production system. Haven't got the details on me at the moment probably around 150-200ppm of N. The other treatments will be pure aquaponic and Aquaponic + Fe chelate (similar to Wilson Lennard's test) 3 replicates of each treatment.

I will be running 3 harvests from each system so if the first crop runs the NO3- down to zero and growth is slow, I may have to add more fish for the second and third crops.

I will be cycling with a bacteria starter and ammonia prior to the fish , then with just fish, no lettuce, for a couple of weeks after that to allow nutrient build up. The lettuce (10-15 per system) will be grown in peat blocks or rockwool to a handle-able size prior to insertion so whilst this is going on the fish can be cycling.

As for reading up, I've read Lennard, McMurty and Rakocy's work along with loads other stuff from the web and forums. As I say it's only a short project so I'm not really setting out to prove aqauaponics is as good as conventional hydro, just grow a few crops of lettuce and discuss differences in the yields, nitrate content of leaves etc.

Sorry to waffle, but this is helping to free up my mental constipation

Hi there Neal, sounds like you have a good grounding by what you've been reading. And no I don't think there is really anything to prove about the validity of aquaponics, but theres certainly lots of work and experimenting that needs to be done. I'd love to hear how your nitrate content of leaves goes as I have heard people worry about that in the past with aquaponic systems but I've never seen anything really conclusive about whether levels are very high or not, rather just guessing that maybe they would be.

Hi Neal,

Have you got any info that youn can share with us regarding nitrate concentration in leaves? Give us a basic over view of the concept.

I'm quite interested, as i can't see why plants grown in aquaponics water would have higher concentration in leaves, as the nute solution that you mentioned was at 150 - 200 ppm and i think the aquaponics water NO3 would be be less than or at worse case the same level.

Eager to learn something new

Steve

Hi Chaps,

The nitrate content of lettuce is monitored as it could potentially be harmful.

Some experiments have been carried out in standard NFT recirculating systems that suggest slightly more nitrate ends up in the leaves than in soil grown lettuce. It is also light dependent, with more NO3- content in decreased light levels - more of a problem in UK latitudes, and as my project will run from August through to November I thought it would be interesting to see how the nitrate content changes over the months in each treatment.

Do you guys reckon 4 goldies will support 10 lettuce, or do you think I need more fish?

Neal

Thanks neal, interesting.

I'd say at least 8 goldies if not more, but Earthbound has the hands on to give you a practical answer


Steve

Were the lettuce plants in the NFT recirc. system planted at the same density as those in the ground? I would imagine that because the nitrate concentration in this recirc systems is substantially higher than in the ground coupled with a more favourable environment for faster and higher levels of fixing that if they were planted at a density the same as those in the ground the competition for resources would be not be such an issue allowing them to assimilate higher levels of nutrient. I would imagine that if one was to compensate for this by increasing the planting density the distribution of resources would be more frugal they-by avoiding this issue.

Mmmm, was it in 80L of tank Neal? I guess it all depends on the size of the goldfish, if they are only say 50mm long, I'd be looking at 8-12 even anything up to 20 or more, to get fairly good growth in your plants, you can get by with less, but the growth rate of the plants won't be as good as it can be.