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I'm going to have to agree with Nate, here. Nitrosomona bacteria don't "need" carbonates as they extract carbon from atmospheric CO2.
Also, let's say you add carbonate...CO3...it nabs a proton from solution...becomes HCO3...nabs another hungry proton from solution...becomes H2CO3...then that just chills out in your system, doing nothing for no one except raising solute concentration. That's like putting all the kitchen and bathroom garbage bags into a dumpster sitting in your living room. The garbage hasn't left the house, just as the H+'s are still there.
Now, let's add KOH or Ca(OH)2. They both dissociate...OH- sucks H+ from solution, becomes water, and can either contribute to the system or evaporate. The K+ or Ca++ are minerals taken up by the plants.
I'd like to know what reference is used to state that bacteria require carbonates. The U.S. Department of Energy states that the bacteria use atmospheric gases...which is why it's important for grow beds to ebb and flow.
Leave it for the hydroponic tinkerers... and the snake-oil slaesman...
Harold .."Oxy-Cal"... or Calcium Peroxygen.... is supposedly used (in hydropoinics)... to provide extra root zone oxygenation... similar to the use of hydrogen peroxide....
Essentially its CaO2.... Calcium Dioxide.... which is falsely.. also claimed to act as some sort of pH buffer... but thats not really true... or at least in the form suggested...
To act as a pH buffer the oxygen would need to be released, and combined into a "hydroxide".... ala Calcium Hydroxide... "slaked", or "hydrated" lime as is commonly used... as a pH buffer...
The "blurb" about "oxy-cal" also suggests avoiding mixing with phosphorus... as iit will effectively precipitate the Calcium out....
Use alternating Calcium & Potassium compounds to buffer in aquaponics.... if you use "hydroxides"... then also alternate with a "carbonate", or "bicarbonate".. of either Calcium or Potassium.... to provide carbon food for the nitrifying bacteria
Nate: " Understanding carbonates is probably the most essential and overlooked aspect of starting an AP system."
Providing calcium necessary for plant growth in AP solution is usually in carbonate form. However, the buffering side effect of this process has to be regulated in order to optimize nutrient uptake and prevent deficiency symptoms in plants. At the 6 ppm -6.3 ppm range we maximize macro/micro uptake by plants and prevent deficiencies normally shown by plants at higher PH levels. A caution with low level PH is that, Crop density/nutrient demand will have to be considered to avoid nutrient depletion Also, lower PH levels safeguard fish from ammonia spikes.
I'm looking at this possibility for AP;
@Harold... a "carbonate", or "bicarbonate" compound....
Most commonly... and beneficially... Calcium or Potassium Carbonate/Bicarbonate...
So what is a carbonate compound?
Comment by RupertofOZ on September 1, 2012 at 8:20pm
But also periodically adding a "carbonate" compound is both necessary, and required.
Using a "carbonate" compound periodically doesn't remove, or restrict your pH control, any more than using the other pH buffer compounds mentioned.
Thanks Nate for posting this video. Great guide for all, removing the ambiguity around the falling PH in AP systems. 50/50 that's the way to go!
It's more correct to refer to "dissacssociation" when talking about processes in aquaponics, whereas an artificial concentrated chemical mix such as a hydroponic solution., with rising pH and temperature, can lead to "association" of chemical ions, and hence "precipitation".
"Precipitation" is not problem in an aquaponics context to even an enth degree of what can occur in hydroponics.
It's correct that in general, Calcium, Potassium and Sodium ions (particularly), are readily inter-changable and distinct relationships certainly exist between Calcium and Potassium. But generally also in conjunction with Phosphorus, (its a long and complicated interraction)
IMO Dolomite Lime is far preferable as a means to address any "magnesium" deficiency, than Epsom salts, primarily because high levels of "sulphates" can cause other problems to plants.
"Carbonate" is not your enemy, unless in a context of high carbonate hardness, high pH, and trace element lockout.
In fact a degree of carbonate hardness/buffering is required in your system, for both fish growth and plant growth, from the Calcium content. But also for the bacterial processes, from the Carbon content of the carbonate.
Using alternating Calcium and Potassium hydroxide compounds to address falling pH.. and to provide mineral needs for plants growth is entirely good, and suggested practice and will address the pH issue.
Carbonates are not necessarily your "enemy" in an aquaponics system, other than in relation to trace element lockout due to high source water carbonate hardness, high pH related issues.
An aquaponics system running within preferred pH range, with a quality fish feed, should never really exhibit any great mineral deficiencies, particularly of elements such as Iron, Magnesium, and some of the more esoteric trace elements.
The Calcium and Potassium buffers used to address the pH issue help replace the removal of these elements due to fish and plant growth, and promote further growth.
But a "carbonate" buffer is still required to replace the "carbon" removal, and promote growth of your bacterial colony.
Sorry Nate but I'm going to take issue with a lot of what you say here.
Carbonates, or more correctly carbonate hardness, can be an issue... both in aquaponics, and more particularly in hydroponics.
But it's a factor of high carbonate buffering and associated high pH more than the carbonates themselves.
The high pH, particularly in hydroponics, but also in aquaponics, causes trace element lockout, particularly of elements such as Iron.
A combination of high pH, and temperature, particularly in hydroponics solutions, can lead to precipitation of chemical salts, including (but not limited to) "carbonate" precipitation.
If there is high carbonate ion concentrations within your water,the addition of your hydroponic nutrients can cause iron carbonate precipitation, where the FE2+ ion associates with the carbonate.
Precipitation is not a problem so much in aquaponics, particularly carbonate precipitation, because the high levels of nitrification in aquaponics are continually using available carbonates.
The bacteria consume the carbon in the "carbonates" as part of their growth, as an essential part of their food source.
That's why nitrification can "crash" when pH drops below 6 (roughly), the "carbonate" buffer has been exhausted, hence no carbon is available to the bacteria.
As it relates to aquaponics, unfortunately no. I'm working on some material on the subject but it probably won't be published for some time. I would recommend hydroponic literature on the subject with the understanding that pH regulation in AP systems should typically be limited to KOH, hydrated lime, some dolamitic lime, and natural nitrification processes. Resh has some great information on the subject of hydroponic pH regulation. Beyond that, read water quality texts regarding carbonates and how they impact solution pH. Understanding carbonates is probably the most essential and overlooked aspect of starting an AP system.
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