Backyard Aquaponics
A place to discuss aquaponics

There is the problem

Interesting reading, we're simmilar in needing to know the how and why.

problems arise when we try and "work out why" on a CLAIM....................

I think that a claim can only be made on that if there was a f&d system running parralel to a CF system, same fish same number of fish same feed rate same temp same EVERYTHING.................unfortunatly this was NOT the case.

The CF was a commercial application, and the F&D with gravel was as a uni prjoect in a lab months earlier................

anyone feel free to correct me if i have made a slight error somewhere

Oh really. I was planning to go and dig his (wilson's) thesis out of the RMIT Library. I think I'll have to make it in to Melbourne sooner than I'd planned to check that out.

Stuart

i didn't mention any names And i may have some small details wrong, so don't crucify me but what i posted was to the bes of my recolection.

I think the only way to to really test the argument is to have a f&d, CF and a flood and flow, side by side, identical everything. Then we can truly see a scientific comparison.

My small scale flood and flow did perform better than the f&d in a short time period. My current f&f beds are going great, except the tomato's are out of season. My idea to add broken pots to the bottom 3 inches paid off, and I am seeing no blockages so far. However scale it up and it [u]could[/] be a completely different story, solids are bigger and greater, water flow would need to be greater so would DO. The gravity fed water in my system actually causes visible bubbles on the surface of the gravel so I wonder if that is helping.

Hi Steve,
I do like to know how and why if the answer is out there.. i`m just inquisitive by nature
It`s quite easy to make the square peg fit in the round hole if you`re not careful though. I did try to be as objective and unbiased as possible.

I still take the view that high O2 systems logically should be better for plants and bacteria growth.

Taking aeroponics as the most extreme example of air ratio and everything points to more the air contact the better.

The contradiction is in the trickle tower analogy where, for whatever the reason, it does reduce nitrates and is similar in many ways to FD or drip/trickle beds.
I used one on my slightly overstocked 4ft tank (140L with ~72" fish) to keep the nitrates down, which it did to maybe 10mg/l.
I had no plants in the tank as the clarias tend to dig them up when bulldozing the gravel.
I switched to a recirc pond filter (pressurised type sized for a 1200L pond) when i grew the chilli`s indoors in a recirc dwc tub fed via a self starting syphon direct from the tank, a 2nd pump returned the water to the fishtank. (for reference no solids got to the dwc)
The nitrates in the main tank were much higher (80-100mg/l) and the chilli`s took over the corner of the room even though they didn`t get a lot of light. In fairness, a FD may have done just as well but i didn`t test that.

FF see`s no differences in growth with his "multimode" system where the playing field is relatively level, all types run from the same fish tank and have the same environmental conditions.
I`m not sure if some are further downstream than others, for example, the dwc supply might pass through the FD bed first which changes things.

If there was an easy way to test them side by side we might get some definitive results..or not, as the case may be

keep in mind there may be other variables such as available light. pH. temperature, feed rates, age, size varieties and condition of fish....

If' we're comparing a lab experiment to a commercial system in a different location -- at a different time of year, I can see how a lot of variables could be different.

When I worked at a greenhouse, We ran an experiment growing seedlings with water from three different sources. Someone forgot to water one day and most of the plants died -- however, more plants survived in one group -- that was the more expensive water that we had been using. We ran out of time and the decision was made to use the more expensive water. I always wondered if it was a skewed test -- since we were hand watering, it is possible that whoever watered the day before watered those plants more heavily.... so many variables, so little time.

Very interesting discussion guys. I cannot add much to it, particularly from a techical perspective. I do have the following comments though:

1. My system is F&D and has heaps of oxygenation potential including: a. the F&D action of pulling air back through the media b. the waterfall action of the water into the sump as the beds drains c. the venturi operating on the water return from sump to fish tank.

2. My nitrates are high (up around 160) and have been for months, despite a reasonable amount - but clearly not enough planting.

3. In relation to growth difference between the methods, I suspect that except right at the start as fish size is built up, most people here are not struggling to keep nitrates up - more the opposite I suspect like myself.

Regarding the whole trickle feed thing Hex - I would be most interested in some further description of how you had it isn your aquarium. I'd love to experiment with some methods of additional nitrate removal to help me stock greater numbers of fish to the amount of grow-beds that I can afford.

Again - great discussion. The concept of removing nitrate through degassing has come up here before bu there has never been any remote sense of explanation of how it works (or whether it works). I suspect that if it does, the answer is to be found in recirculating aquaculture circles. I know that the guy that Ausiponic and I bought our tanks off was running high stocking density of Jade Perch in his recirc aquaculture setup nad claimed to have harly ever had to remove water from system. He had ozone filtration and a degassing setup. I think the degassing thingy was the rlevant part - but not real sure how it works. Will do a bit of research.

Does any one know of any research that has quantified the reoxygenation of water in growbeds or through bio filters?

I ask because sometimes what makes sense and how things actually are don't always line up. I read a study a while ago that the most efficient aeration technique was using paddles (like a water wheel). Turned out to be much cheaper/effective than bubblers and other tehcniques. This apparently surprised the researcher.

If the water falling into the tanks and grow beds and flowing out over the standpipes is sufficient to oxygenate the water then you wouldn't need to run F&D for oxygenation reasons.

Mind you as far as I can tell one of the best pros of F&D is that it should cut down your pump running costs.

I think one of the reasons for flood and drain is that the beds are evenly filled with water each time, there are no dry/dead spots, so that all the bacteria gets a dose of food/water/oxygen each cycle

I'm with you there jaymie - and there are lots of other reasons also, including how this type of system handles solids more effectivelly - distributes them.

There`s a lot of speculation how trickle towers remove nitrate, i don`t think anyone knows for certain but practical testing shows they do remove it.

A trickle tower is pretty much a tube (or stack of baskets) filled with an open medium, water is sprayed evenly over the top and it trickles down to the bottom...deceptively simple

It should be easy to add one to an AP setup.. mount it over the tank for a gravity water return.

Mine was simply a ~30" length of 5" dia tube filled with lecca with some plastic mesh at the bottom to stop it from falling out.
Mounted above the tank and driven by a small (variable output) fountain pump with a foam prefilter to keep the solids out. Not exactly pretty but it was cheap and did the job.

Flood and drain does have a lot of benefits as Jaymie points out, even coverage, low maintenance and less pumping power required.

I`d still like to try out a trickle/drip bed idea that surrounds the entire rootzone with a constant supply of o2.. getting an even coverage is the difficult part.
If it fails miserably so be it, i can always convert it into a normal soil bed i guess. The materials won`t cost much anyway.. just a few quid

Is this the link http://www.hydroponics.com.au/back_issues/issue83.html (beware the noise when you open the link) Oh and Steve I think you'll find that the researching of the different methods of CF and FD were run simultaniously.

When comparing growth rates with the different methods of systems I think that you really need a large scale in both terms of area and time. From what I understand the research being talked about here was was caried out over about 12 months. Other researchers have found that aquaponic systems don't mature until they are about 12 months old, and they aren't at their peak until they're 2 years old. This opens a whole new can of worms as to the value of the results mentioned above. Perhaps a CF system matures at a faster rate than FD, giving the better results? Theres a lot more research has to be done before we can fully realize the true benefits and negative aspects of either method.

However as some have already mentioned here, when translating this research from a laboratory, into a home food production model, we're faced with a whole new set of parameters, that aren't necesarily valid when studying the pure science and chemistry of a system.

Personally, after running both FD and CF in a few different variations over many years, I'll take the flood and drain any day over CF. But then when you start talking about towers, you're adding other benefits to the equation like space saving, and perhaps with the verticle growbed there will be better water distribution through the volume of the gravel...

So many variables.....

our towers are trickle flow while everything else is F&D (all happening simultaneously). Half the towers have cocopeat, the other half have gravel. It will be interesting to see if there is any difference in the growth of the strawberries in the two types.

Interisthing thing today my third flood and drain bed made from black poly had some bulging ishues so when i pulled out the tomatoes i dug right to the bottom there was no gunk there was a lot of worms mainly on the bottom 6 in so all in all i will stick to flood and drain

that it will - a scientific experiment in the makeing it is - the kind of stuff we need here - keep us posted J