Nutrient burn?

[wh33t]

Another quick question.

Can plants in an Aquaponics system be "over-fertilized". This is a common problem with hydroponic set ups and even soil gardens when using artificial fertilizers, but can this also happen in an Aquaponics set up?

[badflash]

No. The fish would die long before the plants would suffer.

[wh33t]

No. The fish would die long before the plants would suffer.

So do the plants ever get their optimum fertilizer needs? Excuse my novice-ness. I'm coming from a hydroponic and soil gardening background. In hydroponics you add chemical fertilizers in a specific concentration believed to be optimum for the plant. How is this optimum level hit in Aquaponics?

[urbanfarmer]

Some research has suggested that with enough water flow the plants will still be able to absorb the required nutrients even if the concentrations are lower than what is commonly suggested. That is why previously I had suggested to have constant water flow in the grow bed (in any form, just don't stop it). If you find a better answer to your question, please share. However, I don't think aquaponics has enough scientific research (or specifically applied therein) to have a conclusive answer yet.

[rfeiller]

the nutrient requirements for each type of plant vary, in hydroponics formulations are plant specific, water is maintained at a certain pH, temperature, and hardness with RO water being the preferred solution base. Tilapia require just the opposite of what is preferred by the plants; tilapia are from hard, alkaline water with a temperature in the mid to high 80's. while plants prefer soft slighly acid water in the 60's to low 70's temperature. so one or the other or both suffer from the conditions.
in aquaponics it is quite frankly from everything i've read a crapshoot. the pH and hardness of the water are all over the place, the level of organics in various stages of decomposition is extremely varied, the type of food fed to the fish determines to an extent, what comes out the other end. the type of fish and how they process the food makes a difference, a herbivorious vs. carnivorious animals have different digestive systems, different natural flora and fauna in their intestines process and obsorb nutrients differently. then throw in some red wriggler earthworms into the mix and unless you have access to a lab with unlimited resources you have no idea what is in your water. so what you end up doing is to try to diagnose deficiencies by the symptoms, which by that time the damage is done to your crops. AP with high nitrates of course work great with plants that can tolerate wet feet and high levels of nitrogen do quite well with no chance of burning: i.e. lettuce and a couple of herbs. crops like tomatoes that don't like wet feet and will produce excess leggy foliage with substandard fruit are a different story, but still no burning. your hydroponics experience will come in handy with your knowledge of nutrient solutions. the trick is to find the nutrient balance without killing the fish. and that my friend is the challenge and fun of aquaponics. :D :D

[wh33t]

the nutrient requirements for each type of plant vary, in hydroponics formulations are plant specific, water is maintained at a certain pH, temperature, and hardness with RO water being the preferred solution base. Tilapia require just the opposite of what is preferred by the plants; tilapia are from hard, alkaline water with a temperature in the mid to high 80's. while plants prefer soft slighly acid water in the 60's to low 70's temperature. so one or the other or both suffer from the conditions.
in aquaponics it is quite frankly from everything i've read a crapshoot. the pH and hardness of the water are all over the place, the level of organics in various stages of decomposition is extremely varied, the type of food fed to the fish determines to an extent, what comes out the other end. the type of fish and how they process the food makes a difference, a herbivorious vs. carnivorious animals have different digestive systems, different natural flora and fauna in their intestines process and obsorb nutrients differently. then throw in some red wriggler earthworms into the mix and unless you have access to a lab with unlimited resources you have no idea what is in your water. so what you end up doing is to try to diagnose deficiencies by the symptoms, which by that time the damage is done to your crops. AP with high nitrates of course work great with plants that can tolerate wet feet and high levels of nitrogen do quite well with no chance of burning: i.e. lettuce and a couple of herbs. crops like tomatoes that don't like wet feet and will produce excess leggy foliage with substandard fruit are a different story, but still no burning. your hydroponics experience will come in handy with your knowledge of nutrient solutions. the trick is to find the nutrient balance without killing the fish. and that my friend is the challenge and fun of aquaponics. :D :D

Thanks for the replies guys. I had a feeling it was a big of crap shoot kind of art. That's ok. That's how I prefer it ;)

[urbanfarmer]

the nutrient requirements for each type of plant vary, in hydroponics formulations are plant specific, water is maintained at a certain pH, temperature, and hardness with RO water being the preferred solution base. Tilapia require just the opposite of what is preferred by the plants; tilapia are from hard, alkaline water with a temperature in the mid to high 80's. while plants prefer soft slighly acid water in the 60's to low 70's temperature. so one or the other or both suffer from the conditions.
in aquaponics it is quite frankly from everything i've read a crapshoot. the pH and hardness of the water are all over the place, the level of organics in various stages of decomposition is extremely varied, the type of food fed to the fish determines to an extent, what comes out the other end. the type of fish and how they process the food makes a difference, a herbivorious vs. carnivorious animals have different digestive systems, different natural flora and fauna in their intestines process and obsorb nutrients differently. then throw in some red wriggler earthworms into the mix and unless you have access to a lab with unlimited resources you have no idea what is in your water. so what you end up doing is to try to diagnose deficiencies by the symptoms, which by that time the damage is done to your crops. AP with high nitrates of course work great with plants that can tolerate wet feet and high levels of nitrogen do quite well with no chance of burning: i.e. lettuce and a couple of herbs. crops like tomatoes that don't like wet feet and will produce excess leggy foliage with substandard fruit are a different story, but still no burning. your hydroponics experience will come in handy with your knowledge of nutrient solutions. the trick is to find the nutrient balance without killing the fish. and that my friend is the challenge and fun of aquaponics. :D :D
Yes, it is a bit of a crapshoot... but, some research is coming out slowly. That last statement I made was based on suggestions in research based by the University of Florida. I have also experienced it first hand in a very controlled AP system where I knew for a fact that I had very low levels of nutrients, yet I had phenomenal plant growth.

[rfeiller]

You do know at that high pH much of the nutrients will be bound up and not available to the plants. Dumping acid in the mix will create a high fluctuation of pH until the buffers are neutralized which is hell on both plants and animals. Either RO or DI with cation & anion resins will help you out, use potassium chloride, not sodium chloride to recharge the system.

[urbanfarmer]

I am not sure what you mean by the buffers are neutralized. Buffers occur as speciation of chemicals depending on the difference of their pKa value, and they are never neutralized. The acid you use to change the pH is the "buffer" problem most people observe. For instance, when people use citric acid, it has THREE speciations at close pH levels and will cause buffers whereas HCl or sulfuric acid will not. Of course, when you throw other chemicals in there from tap water, you can get other buffer effects you can't hope to calculate. Unionized distilled water is the best way to go, but most of us don't have the resources for that. RO water comes out ionized, typically. I'm not sure what anion/cation resins are, but I think you might mean the ionization of the water? Or is this a substance you have used in hydro before??

Yes, certain nutrients precipitate at higher pH values; hence, the reason they are not available, but research conducted by UF for commercial applications showed differences in relative yields were not statistically significant. The nutrients were 5-10 times lower at different pH (including 8), and even at 8 the yields were fine. AP systems are quite complex with microorganisms we have yet to realize. Experimentally observed results that seem to defy our common, hypothetical, and theoretical knowledge is what really helps us understand AP better! :ugeek:

[rfeiller]

cation and anion are resins used to exchange different elements replacing say calcium with a sodium ion. they are physical and are used frequently in the water softner and water purification processes with the final product in some exchange systems being hydrogen. a sodium ion exchange with say calcium ions is very common as home water softners.

the buffers i was referring too can be alkaline or acidic. but the primary ones that are neutralized for the aquatic and horticultural industrial are the alkaline. the buffers are what causes the bouncing back of the pH readings, because the alkali has not been completely neutralized by the acid.

it is not uncommon for if a pH is say 8.0 or higher when acid is added (organic matter such as peat with a 3.5-4ph or acids such as citric, sufuric or whatever) the pH will drop, many times only temporarilly, but will bounce back to 8.0 this is the result of the alkali buffers and requires more acid to be added which can replicate the bouncing several times before the acidic buffers stabilize at the lower pH you desire.

of course multi passes of a lower nutrient solution will make more nutrients available to the plant, it's cumulative.

[urbanfarmer]

Oh, you actually meant using some kind of resin. No, I do not recommend this in aquaponics. Less is more! Use less chemicals to get more vigorous and healthy plant growth!

pH buffering is not caused by something that acts on the acid you are adding, but it is the acid itself... citric acid will act as a buffer to lowering the pH whereas sulfuric acid will not... again, it has to do with the pKa value and the species caused by the interactions therein...

There must be something else going on for the pH to bounce from 3.5 to 8.0 because that is an ion differential of around 50,000x TIMES which is an enormous amount... enormous... amount... there really are too many things to consider as to why you would observe this, most of which fall under the category of human error, but without specifics there's no way to tell.

The reason plants can take up nutrients when concentrations are low with more moving water is not because nutrient uptake is cumulative... it's a bit more complicated than that :mrgreen:

[rfeiller]

The resins are in tanks ion exchange resins are used throughout the water Purification industries. In fact much of the time it is part of the bottled watet process. And I disagree about your statement on buffering capabilities of alkalis and acids.

[urbanfarmer]

The resins are in tanks ion exchange resins are used throughout the water Purification industries. In fact much of the time it is part of the bottled watet process. And I disagree about your statement on buffering capabilities of alkalis and acids.
But sir, I don't want to DRINK my AP water... :mrgreen:

Aren't you using RO water? How would you get acids/bases with their conjugates in the water... You have ammonia in the water, but at a very low molar density... Also, you are discussing strong and weak acids, but you don't seem to draw a distinction between the two. You realize they act differently in solutions with or without a buffering solution present, yes?

Here are some good videos on buffer calculations:

Part 1: http://www.youtube.com/watch?v=hWkXoHqHyfs
Part 2: http://www.youtube.com/watch?v=rLPc8Rcxnmk
Part 3: http://www.youtube.com/watch?v=2fvD_kf_KIE

There are many things to consider in the interactions, and without specifics we can't really say for certain. However, it's not magic; there is sound science from which to base our decisions... pH interactions are probably one of the simplest (yet the most important) aspects of our AP systems... :ugeek:

[rfeiller]

as long as the tap water is sierra tap water (melted snow) it comes through at about 7.0pH less than hundred ppm of total disolved solids. i do not us RO at that point. it is when the batch plant mixes in well water that can be over 8pH and tds of 400 or better that i use RO. but all of the water runs through a GAC tank prior to being added to greenhouse plants, koi pond or fish tanks.
the purpose of DI resins is to exhchange out unwanted elements of the water. i do not add chemicals to the water and prefer not to use any buffering solutions such as pH up or pH down that just adds one more thing for the fish and plants to deal with. some prefer to use DI resins over RO it is more convienent when recharged than dealing with a RO holding tank. to me it requires more work because it has a ppm limitation between recharging. it is not uncommon to mix several different methods of dionization to achieve the desired results including multistage distilation or a slow natural form of ion exchange by using acid peat, most of the peat available in stores lacks the low pH of 3.5-4 and can be partially neutralized.