The Nitrogen response

[Stephen Eugene Robinson]

One of the troubles I have had with my aquaponics tank has been nitrogen buildup in the form of nitrates.   Plants need different nutrients to grow.  Limit one nutrient, and that limits the absorption of all of the others.  I guessed that the limiting nutrient might be either potassium, iron, or magnesium, not sure which would make the difference.  I am still not completely sure, but when I dosed with the 3, the plants went into a growth spurt.  It was like putting a green light on nitrogen use, and the nitrogen in the water dropped.  I saw this this morning, and I was very pleased. I think I will try to find a potassium test kit.  My new Nitrate level is 100ppm and has been cut in half, and I am feeding the fish what they will eat.

 

Another thing I found was a hydroponic model for tomato growth from University of Ohio.  I found a couple things I might be doing that is counterproductive.  For one, in the fruiting stage, soil temperature (read that tank temperature) should be around 72, not 78 like I had it, and pH should be around 6 and not 7.

 

Now these are real numbers with real reasons behind them.  So, last night with great sadness, I lowered the temp on my heating elements.  Even more sadly, my power use will go down.  The pain.  I can also relax and let nature take its course with pH.  My buffer costs will go down.

 

Will all this make a difference?  University of Ohio thinks so.  These guys probably have done scientific tests to back up their claims.

 

I am a retired engineer.  I like claims that have substance behind them, but I will also jump into something like Aquaponics knowing nothing about it - Frantic learning ensues.  Angst at not knowing rules my life, blood pumps, web searches happen, and finally - almost as an afterthought, the nitrogen level normalizes.

 

Sigh

 

Now what?

[Vlad Jovanovic]

Yes, but the University of Ohio has a hydroponic research facility not an aquaponic one. 'Dems a little like the proverbial apples and oranges. In hydro, you only have the plants to cater to, so things like a pH of 5.5 or 6 pose no problem whatsoever. In aquaponics however...

Though you can operate your system at a pH of 6, I don't know that you'd want to. It seems like you'd have to have a really keen grasp on the workings of your system and be super vigilant with other aspects of water quality testing and control. So as not to end up crashing your bacterial colony, for instance. In which case what the University of Ohio says wont make a lick of difference to you. 

The different phases of plant growth, including growth spurts, are a well documented phenomenon. Are you sure that you weren't maybe witnessing this? If your plants are going through an explosive growth phase, (and there a few in most of their life cycles) this would explain your drop in nitrates. At a pH of 7 you shouldn't be having too much trouble with iron/calcium, magnesium lock-out.

Potassium is generally a concern during the fruiting stages. Again, in hydro you can limit nitrogen (as well as phosphorous) after flowering and bump up the potassium. But how do you go about limiting nitrogen in aquaponics? People grow great looking tomatoes with aquaponics under parameters that would make a hydro-researcher scream "that is not possible".

There seem to be a lot of things in aquaponics that defy conventional hydroponic wisdom. Many of these things have yet to be studied and explained scientifically (probably because there is as of yet, no aquaponic "industry" to finance such serious studies). Hopefully someday we'll know  exactly why something that just wont fly in hydroponics, works great in AP. 

Seriously, before you contemplate running your system at a pH of 6, ask around, it seems like anything but a "relaxing letting nature take its course" sort of deal. I believe Nate Storey successfully runs his system at a low (6.2 - 6.7) pH and it doesn't appear to be a laidback option for someone just starting out. 

[Stephen Eugene Robinson]

OK Great.  I take from you you recommend pH 7.  You hear different things from different people on this forum, and that's a fact.  It is not possible to know for certain anything in this environment, and to be sure, I don't, but I do look for answers, and when I believe I see a cause and effect, I try to latch onto it.  One fella on this forum swears he runs at 5.5 and occasionally buffers back up, and thinks I'm nuts for trying to control pH.  I have heard this more than once. 

 

In short, it appears people just keep their fingers crossed, not sure of what works and what does not.  This may be the state of this art. 

 

In my experience, I have seen pH trend downward to around 6.  I don't know where it would go after this since I have intervened.  Tomatos seem to like a lower pH, and fish seem not to mind.  Wherein is the difficulty?  Is it just the dirty word Hydroponics?  The only thing the Univ. of Ohio is saying is that tomatos like that pH.  Is it possible that they would like a pH of 6 under hydroponics, and do poorly with it under aquaponics?  Or maybe it is the bio filter.  I didn't think the bio filter did poorly at this pH level.  Maybe I should double check.

 

Maybe what is needed on this forum is to attempt to define what "good" means.  Good would mean pH, Nitrogen level, Potassium level, and maybe a few other variables.  If we could come up with what good was, then some of these comments might actually be useful.

 

So, I propose that you folks who think you have a well running Aquaponic system, what parameters do you think are useful, and what are your current values for those parameters?  If we were to answer these questions, it might just constitute the closest thing to guidance that can be given to someone starting out.

 

This foum then might actually develop some value beyond just air movement.

 

What say?

 

I would be happy to help coordinate and collect any information offered and synthesize a result.
 
Vlad Jovanovic said:

Yes, but the University of Ohio has a hydroponic research facility not an aquaponic one. 'Dems a little like the proverbial apples and oranges. In hydro, you only have the plants to cater to, so things like a pH of 5.5 or 6 pose no problem whatsoever. In aquaponics however...

Though you can operate your system at a pH of 6, I don't know that you'd want to. It seems like you'd have to have a really keen grasp on the workings of your system and be super vigilant with other aspects of water quality testing and control. So as not to end up crashing your bacterial colony, for instance. In which case what the University of Ohio says wont make a lick of difference to you. 

The different phases of plant growth, including growth spurts, are a well documented phenomenon. Are you sure that you weren't maybe witnessing this? If your plants are going through an explosive growth phase, (and there a few in most of their life cycles) this would explain your drop in nitrates. At a pH of 7 you shouldn't be having too much trouble with iron/calcium, magnesium lock-out.

Potassium is generally a concern during the fruiting stages. Again, in hydro you can limit nitrogen (as well as phosphorous) after flowering and bump up the potassium. But how do you go about limiting nitrogen in aquaponics? People grow great looking tomatoes with aquaponics under parameters that would make a hydro-researcher scream "that is not possible".

There seem to be a lot of things in aquaponics that defy conventional hydroponic wisdom. Many of these things have yet to be studied and explained scientifically (probably because there is as of yet, no aquaponic "industry" to finance such serious studies). Hopefully someday we'll know  exactly why something that just wont fly in hydroponics, works great in AP. 

Seriously, before you contemplate running your system at a pH of 6, ask around, it seems like anything but a "relaxing letting nature take its course" sort of deal. I believe Nate Storey successfully runs his system at a low (6.2 - 6.7) pH and it doesn't appear to be a laidback option for someone just starting out. 

[Nate Storey]

Vlad, Stephen is right- nitrates can become limited, not in solution but in plant uptake and metabolism if there is another major limiting plant nutrient (K is most common when hydrated lime is being used to raise pH).  You can impact uptake rates by supplementing scarce or absent nutrients- so what Stephen saw in his nitrate drop was probably a real result of nutrient supplementation of an absent or scarce nutrient.  Now the trick Stephen, is to figure out what nutrient your system needs.  What do you raise pH with?  If it's hydrated lime then I guarantee it's most likely a solution K deficiency.  If you switch to KOH for pH moderation, you'll see a bump in nitrate consumption.  Ca and K compete, in solution so most likely your K is precipitating out.  Have you noticed any plant nutrient deficiency symptoms?  Another one might be Mg.  I would encourage the occasional supp. of epsom salts-magnesium sulfate as well.  

I run two 2000 gallon systems consistently between the high fives and about 6.4.  Why? Because I have massive enough BSA that my nitrification rates are still acceptable.  My systems run consistently between 0.5 and 1.0 ppm ammonia as a result, but that's not enough to impact fish health, and definitely maximizes my plant nutrient uptake.  It lets me push my plants on pretty rigorous schedules and turn out top-quality stuff.  Lower pHs will always perform a little better from a plant production perspective, and if your fish are adjusted it usually isn't a problem!

[Nate Storey]

Vlad, just saw that last part there- you're also correct when you say that this isn't the ideal for starting out!  You want to work into low pH systems slowly and only when you have really really high system BSA.

I think a lot of the things that seem inexplicable about production in AP has to do with more complex system nutrients and nutrient systems- i.e. system organic matter and small niche nutrient cycles- I think that's lot of the reason why tomatoes can be grown so well- they have nutrient reserves in the form of organic matter that isn't measured on meters but consistently becomes available and is tied up in microcycles occuring in the root zone.

[Eric Warwick]

Ok, so hydroponic experiments do "count" in aquaponics because, THAT'S HOW PLANTS GROW. However, if you run your pH too low then a bacteria crash could happen. There are a plethora of reasons why plants don't work sub-optimally. The main reason being nutrient deficiencies. K, Fe, and Mg deficiencies  are actually common so, providing these in a foliar spray you would help the plant grow--take in more nitrates. As for your pH, it's good.

[Nate Storey]

Right-O Eric. Yeah, foliar sprays are great- especially if you're cleaning up a little iron deficiency in a hurry to go to market.  :)  it's kind of a lazy approach to Fe supp., but i do it all the time!

[TCLynx]

The main reason that people recommend a neutral pH for AP is because the bio-filter functions better between a pH of 7-8.  However, most plants do prefer a lower pH.  And the bio filter can still work at a lower pH.

The biggest reason that people are advised to keep their pH above say 6.5, is that the most common pH test kit that people use for aquaponics only measures down to 6 so if it reads 6 it could be 6 or it could be way lower.  The bio-filter may still be working down at a pH of 6 but I have also seen situations where the pH drop way below that and the ammonia spikes up and if it isn't caught and corrected quickly, it can really crash the bio-filter and in some rare but terrible situation, kill the fish and require the system be cycled up again.

So, I've been running three systems for a while now.  One system if full of calcium carbonate and stuck at a pH of 7.6 and that poor system suffers from constant Iron lock out and terrible potassium deficiencies since all the potassium precipitates out, that system will be getting new media eventually.  The nitrates in that system tend to run way in the red during the hot season and during the cool season when more plants grow well here I can sometimes get the nitrates down into the light orange range.

Then I have a 300 gallon system which I made sure the media is all pH inert stone and that system I alternate using potassium bicarbonate and calcium carbonate as the buffers when ever the pH gets down to 6.  I generally try to keep that one in the green range on the API pH test kit and that system is doing very well since I started collecting rain water to top it up.  The nitrates on that system are totally dependent on the plants in the system.  When I let the plants get nice and big I find my nitrates down below 5 but when we rip a big plant out I definitely see the disruption and the nitrates may jump into the red till new plants take over.

The tower system is still kinda new and My rain water collection for that system still needs work so that I can keep the pH/calcium from increasing every time I top up with water.  That system has been running with a pH between 6.8-7.2 mostly and I do add iron and seaweed extract to that system regularly since I still have to top up with well water a bit too often.  The Nitrates in that system are currently about ten but that may be largely because the weather has cooled and we have also removed some of the fish.

[Nate Storey]

That's a good point TC.  If your kit doesn't go below 6, then you really don't want to delve into the unknown!  You could go so low that you have no idea where you're at- I hadn't though of that.  I guess all of this just highlights the value of always testing- especially if you're worried about pH drops and your nitrifying bacteria slowing down. . .  

[Nate Storey]

(I really felt like putting some star trek references in that last post, but i didn't because i don't want you guys to know that i'm a nerd.)  

[Eric Warwick]

Don't worry, I'm probably a bigger nerd than you.

Nate Storey said:

(I really felt like putting some star trek references in that last post, but i didn't because i don't want you guys to know that i'm a nerd.)  

[TCLynx]

Going where no fish has gone before

[RupertofOZ]

Stephen Eugene Robinson said:

OK Great.  I take from you you recommend pH 7.  You hear different things from different people on this forum, and that's a fact.  It is not possible to know for certain anything in this environment, and to be sure, I don't, but I do look for answers, and when I believe I see a cause and effect, I try to latch onto it.  One fella on this forum swears he runs at 5.5 and occasionally buffers back up, and thinks I'm nuts for trying to control pH.  I have heard this more than once. 

 

Stephen, it may have been my post you are referring to... but if that is the case you have misintepreted what I said...

 

Which was that recent hydroponic research suggested a pH range of 5.5-6.2... as opposed to the more traditional 6.2-6.8

I don't deliberately run my systems at a pH of 5.5.... but at times I certainly approach a pH value <6.0 occasionally before buffering back...

My systems all, as do most of the mature systems of seasoned aquaponicists... run consistantly between values 6.0-6.8... and with ammonia, nitrite and nitrate values of 0,0,0...

 

A point on nitrates... nitrates are NOT detremental to fish... unless they exceed (consistantly) a value of 450ppm (bluegill).. for extended periods...

And high nitrate readings imply that, one, your nitrification is working... two, you have opportunity to plant a lot more plants... or three, especially if you have levels of ammonia and nitrite also present... that your system is marginal in terms of filtration for your stocking capacity...

 

 

In my experience, I have seen pH trend downward to around 6.  I don't know where it would go after this since I have intervened. 

 

As you should be observing... and it will continue to fall below 6.0if not buffered back....

And if your pH was to fall below 6.0... it will inhibit the nitrifying bacteria... and probably crash your bacterial colony... leading to a spike in ammonia...

Usyally the first sign this is imminent is a "milkiness" on the surface of your tank..

 

It is a scientific fact that the nitrification process will trend towards acidicy... unless your system is carbonate buffered, by choice of media, by source water... or by intervention of buffer addition...

And  those who suffer poor plant growth, trace element deficiencies and even imbalances in their nitrification processes... almost universely have pH values that reflect a level of high pH... due to carbonte hardness, and sometimes associated general hardness

 

Tomatos seem to like a lower pH, and fish seem not to mind.  Wherein is the difficulty?

Indeed tomatoes are a plant that prefers acidic pH conditions... and within reason the fish will happily adapt... there is some evidence to suggest that fish might prefer higher pH values in terms of optimal growth... but I tend to believe that the research that suggest that.. is more directly related to the methodology of the systems that were researched, rather than perhaps an actual  correlation to pH itself...

Certainly I have not seen any significant degradation in growth rates in my fish stock at lower pH values

 

Or maybe it is the bio filter.  I didn't think the bio filter did poorly at this pH level.  Maybe I should double check.

See above...

 

Maybe what is needed on this forum is to attempt to define what "good" means.  Good would mean pH, Nitrogen level, Potassium level, and maybe a few other variables.  If we could come up with what good was, then some of these comments might actually be useful.

 

So, I propose that you folks who think you have a well running Aquaponic system, what parameters do you think are useful, and what are your current values for those parameters?  If we were to answer these questions, it might just constitute the closest thing to guidance that can be given to someone starting out.

 

This foum then might actually develop some value beyond just air movement.

 

Stephen, and others... I would encourage you to join the BackyardAquaponics forum as well... it is the worlds largest, longest running aquaponics forum... and I've yet to see a questioned asked on this community... that hasn't been asked, and answered... many times before on the BYAP forum...

http://www.backyardaquaponics.com/foruum/