Backyard Aquaponics
A place to discuss aquaponics

If so why???.... nitrates just aren't a problem, in terms of fish... unless exceeding values of 500 ppm+....

And I've never seen a situation where, in aquaponics.... the plants don't just gobble them up...

Unless you just don't have enough plants.... but almost always, that means you don't have enough filtration capacity anyway....

Besides the filtration provided... that's the main purpose of media filled growbeds... to grow plants with the nitrates....

I would say to have the ability to manipulate the nitrate levels depending on the crop I am growing rather then reduce.

Rupert- The reason I prefer to have the ability to manipulte my nitrate levels is that when im growing tomatoes or other heavy fruiting crops, you can produce a larger yelid with lower nitrogen as they can take up more phosphorus. High nitrogen levels keep them looking nice and dark green and they grow robustly, but wont flower anywhere near as much as if you lower the nitrates.

UVI regulates nitrates by the frequency that they clean their netting... this is kind of similar to that. Less cleaning of the filtration media creates anerobic zones which convert nitrates to Nitrogen gas thus reducing nitrate levels overall in the system.

Ahhh... some interesting points there Ryan... and I respond in general terms for the benefit of discussion...(much of which I'm sure you know)... not as anything personal...

IMO... the level of phosphate requirement for plants ... is greatly over-inflated... as a result of decades of depleted soil agriculture practices... and subsequent high phosphorus fertiliser applications... being transferred into backyard gardens...

And is actually more a function of pH more than anything... {Notes and emphasise inserted in quotes by myself}












So, where am I going with this Ryan…

Most raft systems are modelled on the UVI systems… with solids removal…

And most people overlook several, what to me, are important caveats…

Solids removal – which decreases not only trace element provision, but lowers phosphate availability
UVI supplements their systems with the addition of trace elements
UVI principally grow lettuce and basil… both IMO, low phosphate, low trace element requirement crops, principally requiring only nitrates…
UVI manipulates nitrates according to plant selection
UVI systems are generally within a pH range of 7.5 – 8.2

A recent study of growing aquaponic lettuce in Thailand compared growth rates of “filtered” and “non-filtered” water…

http://api.ning.com/files/DIfOCTf0mqPgs ... riment.pdf

What I found interesting in the paper cited... was the fact that yields increased in the filtered water... with a corresponding decrease in Phosphate levels due to the filtration...

That doesn't surprise me at all... particularly with lettuce... which just doesn't need a large phosphorus provision... basically just nitrogen and water....

IMO... the same applies to most plants.... and the case for high phosphorus NPK fertilisers, utilised in old style agriculture,... is more to do with soil pH and phosphorus retention/leaching....

Commonly, soil based agriculture applies both lime and superphosphate.... chasing it's own tail so to speak... And I say this because most pond based aquaculture applies lime to "spelled" ponds before refilling.... to release the phosphorus laid down by wastes during the previous grow out period... phosphorous that is otherwise "bound" or "retained"...

And the study is a case in point... a pond based aquaculture system... with (no doubt) lime applied... and reflected in the pH... principally for pond base algal bloom management techniques...

I truly believe that phosphorous , while traditionally considered a "macro" element... is actually more a "micro" element... for most/many plants...

And, as is the case with most AP systems... in acidic pH conditions... is freely available for uptake in the "micro" amounts needed by plants...

Most pellet feeds contain all the phosphorous needed in an AP system IMO... and a balanced flood & drain media, well oxygenated system, with worms.... is all that's needed...

In raft based systems... within a pH range of 7.5 - 8.5... many "phosphorus" related issues... are actually a direct result of the pH range...

And indeed, your observations regarding the colouration, and growth, of your tomatos... are more a reflection of your pH... and phosphorus lock out... rather than the need to manipulate your nitrate levels...

Personally... I think you would be better off manipulating your pH to within the range of 6.2 - 6.8... ala hydroponics... rather than manipulating your nitrate levels...

And giving them a Potassium boost at the flowering stage...

You may also note the "quoted reference to ammonium.. rather than nitrate s.. with regard to phosphorus uptake...



Suggesting that in fact phosphorus uptake is more a function of the ammonium ion.. rather than nitrates... which would imply that you should in fact be increasing your feed and running a trace ammonia level... rather than reducing your nitrates...

Unfortunately, unless you're running a pH between 5.2 - 6.8... this isn't possible for reasons of toxicity...

But this exactly what occurs in hydroponics... where most Part A nutrient mixes... are actually just urea... which converts to ammonia/ammonium... within the pH range mentioned... and the Part B nutrient mixes are primarily trace elements... with very little phosphorus...

LINKS
http://www.back-to-basics.net/efu/pdfs/phosphorus.pdf
http://www.oznet.ksu.edu/library/crpsl2/c665.pdf
http://www.ipni.net/ppiweb/bcrops.nsf/$ ... 9-1p06.pdf
http://api.ning.com/files/DIfOCTf0mqP-g ... riment.pdf

Nice to hear from you Rupert and I don’t take any offense. There is some great information here and it’s nice to see people using their heads 
Let me first start off by saying every system seems to have its caveats. UVI has buffer additions, Flood and drain beds take a large volume of media, space for filtration and a large sump, NFT can clog and die quickly during a power interruption, vertical towers can clog, etc. I have tried to incorporate different aspects of AP into my home system to improve on older designs with known flaws.

I haven’t read the Thai paper (which I will do later) but I agree that it would be of no use if I was only growing lettuces and leafy greens. I am sure the filtration method will have to do with the decrease in phosphates but again, I’ll read it tonight. I also agree that PH is a huge factor in nutrient availability and religiously keep my system running between 6.7-7.0 (Usually 6.. I have no doubt that there is enough phosphorus in the system to grow plants and get fruit but I have tried it both ways in previous years and the results spoke for themselves. There is a noticeable difference (at least in my system) in fruit production in a lower nitrate environment at the same PH level (~6. as a higher nitrate environment. Back when I was growing hydroponically there was a noticeable difference in blooming a plant on low phosphate high nitrogen “grow” fertilizer vs high phosphate low nitrogen “bloom” fertilizer while both formulations were kept at the same PH. I agree PH can throw things off, but at the same ph…side by side…there is still a noticeable difference in production whether grown aquaponically or hydroponically. I don’t advocate anyone runs a system over 7.0 unless they are growing a specific high ph crop or are trying to cycle a new system faster.

“UVI systems are generally within a pH range of 7.5 – 8.2”
As far as I know, UVI keeps their PH in the 6.8-7.5 range but I’ve never heard of them running it into the 8’s. That’s a lot of lock up, I definitely wouldn’t suggest running that high.

“There is a marked increase in phosphorus uptake in the presence of ammonium nitrogen in comparison to nitrate nitrogen”
This is kind of comparing apples to oranges imo. It discusses uptake in the presence of ammonium VS nitrate, but doesn’t say anything about uptake in say 200ppm nitrate vs 50ppm nitrate. Manipulation of ammonium concentrations to increase phosphate uptake would be another area to delve into and I would love to see something written on it (or run some trials myself in the future)

I don’t claim to have a laboratory grade aquaponics research system where I can take spectrophotometer readings 3x daily and plot data over the course of years but I do have enough control of the environment and testing equipment that is accurate enough that I can gather information and make changes based on my observations which is what ive been doing. I will say there is always room for improvement in any system so I welcome all of the discussion

Some interesting food for thought. Rupert you've obviously given this a great deal of thought. My hats off to you, I would not have considered looking at the phosphorus levels in relation to soil farming practices.

Ryan, it wasn't clear to me whether your system was running hydroponically or aquaponically or maybe both when you looked at your plant growth under high and low nitrates? With your aquaponics setup, is there a particular nitrate level you are shooting for? Thanks.

You'll get no argument from myself, or many other senior members, about the benefits of running an AP system within a pH range of 6.0-6.8....

Indeed myself, and others with mature systems.... consistantly run (stablely) around the 6.0 mark....

But just as consistantly.... we run with zero nitrate readings.... with the plants taking all available nitrates... especially tomatos which have been proven to be heavy nitrate feeders...

I've not had, nor have others from what I've seen posted... any problems with growth, or fruiting in tomatoes in AP...

Now, I'm talking flood & drain media filled grow bed systems... rather than raft style systems with solids removal... so it might be hard to do some comparisons...

But I'm still not sure why, with solids removal... you might be running high nitrates in your system anyway... it would seem to suggest that you don't have enough plants utlising the available nitrates... or to put it another way... you're under utilising the available nitrate levels...

Just what levels of nitrates do you run....???

I note your references to "blooming" crops in hydroponic conditions... and the results you noted...

But wonder what the results might have been in a low nitrate/low phosphorus system... and whether or not the results were plant "type" specific...

While I understand the principals and some would say benefits... of solids removal in raft systems... I've never understood why people adopt such a methodology when it requires addition of trace elements, or in your case manipulation of nitrate/phosphorus levels.... when a media based flood & drain system... just does it all without any necessary intervention...

Taking stuff out of the loop... just to add it back... doesn't make a lot of sense to me... although I appreciate the solids removal from a filtration aspect...

I'm still unconvinced as to the need to manipulate phosphorus levels in general.. or even nitrate levels... when either might actually, perhaps not in your case with your pH... be more a matter of pH in any case... or the design, and/or methodology adopted...

Wow. Looks like I pushed a button. Really set you guys off. LOL.

But, then again, this is why I read this forum. Everyone has tons of info in their heads from experience, training, screwing up, etc... The more everyone shares, the more informed the rest of us will be.

6.6 Billion people in the world (probably more by now). I only want to feed a small portion of them. Starting with my family.

Before AP, I grew a lot of hydroponic crops(Tomatoes, Eggplants, Cone flowers, sunflowers, zinnias, dandelions, panseys, leafy greens, tons of other stuff) and did some side by side testing with different nutrient lines to satisfy my own curiosity. Years later when I started to venture into AP, I read an article that described phosphate uptake in plants under differing nitrogen levels (in soil) and had resulting pictures. It's been years and I cant remember the source or if they gave PH values but reading the article brought that thought of low nitrogen, high phosphorus for fruiting back into my mind. Since I was building a new system, I decided to design the filtration to have the ability to manipulate nitrate levels just in case I ever decided to do a crop specific harvest like all Tomatoes (which i ended up doing a year later). If I have a big variety of greens and fruiting plants growing at the same time, I don't even pay attention to nitrates, I just stick to my feeding schedule. When I did the tomatoes, the levels started at ~100ppm (or greater, didnt do anything special to the water) until they started to flower and after a month of flowering, I decided to try dropping the nitrates and see if things sped up. New clusters started forming all over the place and I saw a noticable difference in fruit production for the rest of the season while keeping the nitrates at roughly 20ppm. Right now I have a variety of things so I dont keep track of nitrates but if I was planning on doing another straight tomato crop or eggplants or something like that, I would keep a closer eye on things.

Now, could it have been something else? Sure, there are so many processes going on that it would be difficult to say for sure that the difference was 100% b/c of the nitrate drop but the PH was stable, and the only thing I changed was filter cleaning frequency (which in turn changed nitrate levels). The plants (different species though) could have all hit a growth spurt and just taken off coincidentally with the timing of my nitrate reduction but it just seems to convenient that something like that would happen.




At 6.0 I don’t imagine you have a whole lot of nitrification going on so maybe that has something to do with your undetectable nitrate readings? At 0 nitrates, couldn’t the tomatoes be better utilizing phosphorus for fruit production which is kind of what we are talking about here? Id at least say it is a possibility.

I also agree that there will be major differences between flood and drain styles and raft style so comparison is a little tricky but I appreciate the discussion.

I run a heavy pretty heavy fish load (about .6lbs/ft^2 when doing the tomatoes) but it changes throughout the year as fish size changes. I don’t remove solids very often yet my filtration has enough area that I don’t end up with anaerobic zones until I am very close to cleaning them out so I imagine I am getting further breakdown and conversion to nitrate from the residual waste in the filters. I had to let them get pretty funky to get the nitrates to drop that low (and also made a little nitrate dropper out of a long airline tube but that’s a story for another day).

Last time I took a nitrate reading I was sitting around 100ppm with mixed crops thriving.

Could it have been the specific crops I grew in hydro? Sure, anything’s possible but it’s not like I did coneflowers and that’s it. Would have loved to run a trial with low N low Phos fertilizer but a little too late now.

I also want to be clear, my system didn’t require manipulation of anything to grow the crop, I just thought it had the possibility to grow bigger/better/faster with a few changes. I am a perfectionist at heart and I know everything can be improved upon so im always going to be changing this and that until I find something better. I am sure there are a lot of improvements we can still do to a flood and drain beds that haven’t been thought of before. As simple as something like that is, there are so many small intricacies that there will always be room for improvement.

As for the why people want to use rafts over Flood and drain beds, people could go back and forth all day with pros and cons. I like the ability to move/space crops out if need be, harvest of the entire root system for long shelf life, ease of harvest in a commercial application, etc. With media I love the introduction of worms into the system to break down waste, love the simplicity of everything and the ability to grow root crops. I try to incorporate both methods into my system. I just say do what works for you.

You'll get an arguement from myself, F&F... and many other senior members about that Ryan...

While I do adjust my systems back to about 6.4 whenever I actually get around to measuring the pH.... my systems consistantly run at 6.0.... as do many other member systems....

And with consistant abundant plant growth.... see my system threads....

And, with an above average biomass, and heavy feed rates.... I can assure you that "nitrification" IS "going on"... and entirely efficiently...

If it wasn't.... I'd have constant elevated ammonia, and/or nitrite spikes.... or dead fish...

Whereas, in a well balanced flood & drain system.... it is entirely common to see readings of 0,0,0... ammonia, nitrite, nitrate......



Ryan, from all my readings, not only in AP, but hydro and soil gardening... it is Potassium that both sets fruit/seed and is directly responsible for yield...

And I usually add a Potassium boost at flower set for that very reason...

Phosphorus is more related to overall plant health/growth... and in interaction with nitrogen.. for leaf developement... due to it's importance in photosynthesis...

I bet if you looked at the analysis of your "bloom" nutrients... you'd find a healthy Potassium content....

Sorry... but I believe the importance of "phosphorus" is entirely over-stated and accepted in our physcie from agricultural practices to supplement over-worked/depleted soils...


I haven't got a problem with that Ryan...

P.S ... For many years I always ran my grey water from the laundry onto my tomato patch... in the belief that the phosphorus would be benficial...

For some years, since the introduction of "phosphate free" laundry powders.... I've still continued to do so.... without any significant noticeable difference in growth/yeilds at all...

If anything... the growth and yields have been slightly better....

But even in my soil gardening... I added a Potassium boost at flower set...

Rupt said You'll get an arguement from myself, F&F... and many other senior members about that Ryan...
yep i agree with Rupt
Aquaponics is a whole new learning curve what worked with something else need not work with Aquaponics

I know this is an old thread, but bringing the discussions back up. Rupe - How do you add your potassium to your AP system?

Rupe is no longer a member here Chris.

Hmmm... Can anyone else chime in on the addition of potassium to your system?

Potassium bicarbonate...

If adding for deficiency reasons then 1x level teaspoon per 1000L of water. It will raise your pH a little, so I wouldn't use it if your pH is above 7.0... in that situation you could use Potassium sulphate.