Saturday, June 23, 2012

Here's the problem!

After experiencing what appeared to be an iron deficiency I began adding MircobeLift Iron Cheate 60ml at a time.   The levels would come up slightly, and then drop out of sight and the plants were not looking any better.  When I began to run out of MicrobeLift I shopped locally and found Dr Iron which boasted 8% iron chelate.   I had my doubts and so I tested the strength of two iron chelate products.  MicrobLift does not specify the percent and I think I know why.  Here's the results and my method of conducting the test.

I started with 0.5 ml
added 200 ml of distilled water
this gives me a dilution of 0.5/(200+1) = 0.00249

then taking my next sample from this dilution, I repeated the procedure resulting in a 0.00000622 dilution.

Assuming the product is 8% FE+ as claimed then two dilutions results in 0.5 parts per million which is mid scale on the FE test.

Here are the results of testing equal amounts of both MicrobeLift and Dr. Iron

This first picture shows the Iron  and the second shows the Chelate Iron

Dr. Iron = 0.25 ppm
MicrobeLift = 0.0 ppm

Dr. Iron => 1.0 ppm
MicrobeLift = 0.0 ppm

I tested a stronger sample of Microbelift and verified a trace amount of Iron Chelate, but Dr. Iron is less expensive for more product and provides a substantially more concentrated dose of iron chelate .  In fact Dr Iron contains over twice as much Iron Chelate as they advertize! But it's in the form of EDTA which requires a low pH.

MaxiCrop Seaweed with Iron claims 2% iron chelate and is a favorite among other aquaponic enthusiast, but I did not test that product. 

Here are the real world results.    In the weeks ahead of switching to Dr Iron I had applied 1-1/2 bottles of MicrobeLift with meager results.  Two days after using just a small amount of Dr Iron the plants have begun to show obvious and rapid improvement.

Dr. Iron  2012-06-23_1731
Dr Iron 2012-06-24_1810
I have continued to add 25ml of Dr Iron to the 1000 gallon system once per day and when I add the iron I pour it directly on the Hydroton as I did with the MicrobeLift.

Today is Tuesday June 26 2012.
This morning's test showed that the level of chelated iron was nearly the same as yesterday!  The chelated iron may be normalizing after only three days of dosing with Dr Iron as opposed to MicrobeLift.

While the two beds show a significant difference in growth, the raft system has become healthier and is showing a lot of promise.  The foliage has become green and the plants are beginning to grow again.

Dr Iron is a far superior product.  I'm guessing MicrobeLift is making an effort to sell something that will not change the color the water in an aquarium.  But I think they should state the percent in order to be more honest about the product.

Dr Iron has caused my water to take on a brown color, but this is a aquaponic system not an aquarium so to really is not important.
The tomatoes have grown up around the basil since my last photo.  The basil on the left is from the raft. 

Look at how much the basil in the gravel has grown!

This is the basil in the raft.  It has regained most of it's color and it doing much better since I switched to Dr Iron

The raft is clearly stunted and anemic, but I have hopes of a full recovery
Dr Iron is great, but it may not be available. So I'll address iron products in general.
This is from Green House Grower
There are many chelating molecules available, but only three that are commonly used in horticulture: EDTA, DTPA and EDDHA. These abbreviations refer to the chemical structure of the organic molecule. In general, manganese, zinc and copper chelates are only found in the EDTA form. In comparison, there are three forms of iron chelate, FeEDTA, FeDTPA and FeEDDHA, although the most common form is FeEDTA.
With iron nutrition, the form of iron is very important. The three common chelated forms (iron-EDDHA, DTPA and EDTA) differ in their ability to hold onto the iron (and therefore keep iron soluble and available to plants) as the media pH increases. Between a media pH of 4.0 to 5.5, any form of iron will work (including iron sulfate) at supplying iron to the plant. However, as the media pH increases above 7.0, only the iron from Iron-EDDHA has high solubility. Research has shown that the ranking of iron forms from most effective to least effective at supplying iron at high media pH is Iron-EDDHA > Iron-DTPA > Iron-EDTA > Iron sulfate. If iron is applied in a form that is not soluble because of high media pH, then most of the nutrient will not be available to plants until media pH is lowered.

In general the best products will say EDDHA because they work over the widest range of pH

This article at may also help while shopping for an iron product
Other less-expensive products are also available. One widely sold product, Ironite, contains iron sulfate.
Holt explained Ironite has a "high sulfur content that helps to temporarily acidify the soil around the plants, so work it in around the plant, and then water it in. It works well on turf and on some plants if the soil pH is not too high."
"Another product we sell is called Dr. Iron," he said "It is 22 percent iron and 55 percent sulfur. It basically takes iron oxide and covers it with molten sulfur. As the sulfur dissolves, it releases the iron."
IronSul Soil Acidifier with Humic Acid is another way to treat chlorosis. It is acidic, so it lowers the pH, making the iron more available. It also has a small amount of zinc to supply that micronutrient.
Foliar sprays to the leaves often produce a quick response, but they are inconsistent and temporary.

Tuesday, June 19, 2012

Are These Rocks Nutrient Theives?

This is one of the most important technical posts I have made.  First I will describe the situation leading to the what caused these plants to show different states of Iron or Magnesium deficiencies.  Please bear with me or skip to the last update of 2012/07/10

Beginning Wednesday 13 June 2012 I began foliar feeding chelated iron (FE2+).

On Monday 19, June I measured the FE and FE2+ in the water. 
Both were zero.    This amazed me because when I started the system I added 120ml of MircobeLift Chelated Iron to the system.

In the above photos you can clearly see a difference between the plant from the raft on the left and the plant in the gravel on the right.  Both share the same water.
Sunday 17, June - pH=6.4, Ammonia=0.25, N2=0, N3=0.5, PO4=10, GH=7, KH=1, FE=0, FE=0.0 mg/L, FE2+=0.0 mg/L
Sunday  after measuring the iron I added another 60ml MircobeLift Chelated Iron.   60ml is the recommended dosage according to the instructions on the bottle.
Monday 18, June - pH=6.4, Ammonia=0.5, FE=0, FE=0.0 mg/L, FE2+=0.0 mg/L
On Monday I added another 60ml and finally got a reading of FE=0.0 mg/L and FE2+=0.5 mg/L .
Just a side note about the Hagen Iron Test.  I don't like the test tube because it has a round bottom, and the cheap stand does not provide a place to hold it.

Here are photos taken the morning of Tuesday 19, June.

Clearly some improvement.  Not that I'm impatient; it will take time, but overall the deficiency is still evident.  About a week ago the plants in the gravel were somewhat yellow and pale when they were transplantded from my indoor grow bed, and given a large dose of MirobeLift Iron.  They suffered a little from the transplant, but soon recovered.  When the plants in the raft continued to pale I became more concerned, and  took these steps to correct the problem.

Tuesday 19, June pH=6.4, Ammonia=.25, FE=0, FE, FE2+=0

It seems that the problem has not yet been resolved. 
Tuesday morning I added another 60ml MircobeLift Chelated Iron
I'm nearly out of MircobeLift Chelated Iron so I hope to find the time today to buy some MaxiCrop Chelated Iron.  I think it's available at Lowes or Home Depot.

UPDATE: The  MircobeLift Chelated Iron was found to be an inappropriate product for this system.  I have documented the difference between this and another product IN THIS LINK.
MircobeLift Chelated Iron is suited to aquariums not aquaponics where vegetation is more important than the color of the water

UPDATE - 2012/07/10:
Here is what I've learned with the help of  Vlad Jovanovic.
Much of what follows was taken directly from Vlad's conversations with me.  I have changed some of the wording to put it into this context, and hope I have not misstated any of what he told me.
Without Vlad's patients and kindness I would never have been able to post this topic.

A lower pH is required for FE2+ uptake by the plants because the organic acid (the chelating agent) keeps the FE2+ bound in that ferrous state long enough for the plants to utilize it. Otherwise the ferrous iron will begin to precipitate out of solution and stick to the rocks and walls of the tank.
But the water was shared with and flowed from the raft into the gravel so why then did the raft exhibit the worst symptoms of FE2+ deficiency?

CEC or Cation Exchange Capacity, refers to the quantity of negative charges in soil existing on the surfaces of clay and organic matter. The negative charges attract positively charged ions, or cations, hence the name ‘Cation Exchange Capacity’.

The rocks have a higher CEC than the water which most likely has a CEC near zero.  This may have attracted the FE2+ through the opposite change and caused the FE2+ to accumulate on the surfaces of the rock, .and since there was not enough of it in solution to go around CEC played a role in helping the media bed plants to exhibit less dramatic signs of iron deficiency.
The cause of the Fe2+ becoming unavailable is essentially in a word...oxygen. Without any sort of binding agent (or 'chelating agent', remember those terms are interchangable...) the 'un-bound' Fe2+ will revert to plant un-usable a matter of seconds. That is why it is important (again, in the homemade variety) to 'chelate' the Fe2+ with organic acids i.e tannins from Oak leaves or whatever. Otherwise the 'window of opportunity' for your plants to use them is small (seconds/minutes as opposed to hours/days). 
Temperatures and pH play a role in this scenario too, helping to either delay, or speed up the conversion of Fe2+ to Fe3+...but oxygen is the 'culprit'. The tannins and lowish pH help 'protect' the effects Fe2+ from oxygen (could be one easy way of looking at it). Remember iron is a transitional metal, so just converting rust (Fe3+) to Fe2+ without Oxygen with an RSG (Really Smart Guy) filter isn't enough. You have to keep it that way long enough for your plants to use it.

But in the end the CEC wasn't the root cause of all the plants showing an iron deficiency.  Without it the plants may have looked pale and yellow, but the root of the problem was not enough Fe2+ in solution. (Due to the bunk product I was using at first).

There may or may not have been a Magnesium deficiency as well. (Vlad says probably,... but we'll never know since I added the Epsom salt and lowered the pH around the same time as switching Fe products)...pH is real important to bio-availability of many plant essential elements.
Remember Chelation does not involve a transfer of electrons, but instead it is the ability to bind the iron compound in the ferrous state. The ferrous and ferric transition happens when iron compounds change states of oxidation. It is a low Oxidation Reducing Potential (ORP) that will tend to unbind the ferrous FE2+ and allow the compound to transition into a ferric FE3+ state because of the availability of oxygen. 
Whereas a high ORP with organic acids will act as the chelating agent binding, and keeping the iron soluble and non-reactive with the oxygen.

The raft is recovering nicely 2012/07/08
I hope this helps you to understand the way pH, temperature, cations and the CEC, Oxidation Reducing Potential (ORP) and chelation work to provide and available nutrients.
 I will continue to update this post if any more information comes to light.   

Here is a good article from Nate Storie at Vertical Food Blog

Friday, June 8, 2012

Assimilation of Nutrients

Wishing to understand water chemistry I began reading about REDOX and pH but the topics became overwhelming.  So I decided to take notes starting with definitions, because so many acronyms were being thrown at me all at once.

Then I tried to get my head around why it's called Reduction and what was being reduced.

Finally I began to understand that most of this water chemistry topic is about electricity and ions.   So here are my notes.  I've had some help along the way from a couple experts and Dr. George B. Brooks Jr. helped me convey the acidic reaction even better than I had.

Beyond the text I've quoted from various internet sources I have added some commentary in red italic. 

Without the ability to gain electrons many minerals cannot be absorbed and properly assimilated.


Ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge.   [1]
Ionization is the process of gaining or losing electrons from a neutral atom or molecule  [1]
anion is a negatively charged ion 
cation is a positively charged ion  [1]

Oxidation - involves the loss of electrons or hydrogen OR gain of oxygen OR increase in oxidation state.  [2]
Reduction - involves the gain of electrons or hydrogen OR loss of oxygen OR decrease in oxidation state.
The species that gains electrons is said to be reduced because it has less voltage and less potential to oxidize.

CEC or Cation Exchange Capacity, refers to the quantity of negative charges in soil existing
on the surfaces of clay and organic matter. The negative charges attract positively
charged ions, or cations, hence the name ‘
Cation Exchange Capacity.

ORP stands for Oxidation Reducing Potential and is sometimes referred to as REDOX (Reduced oxidation).
is the tendency of a chemical species to acquire electrons and thereby be reduced [3]

TDS stands for Total Dissolved Solids. 
creates the pathway for the “ionization” (or more correctly electrolysis) to occur. [4]

pH stands for "potential hydrogen”.
measures alkalinity or acidity on the pH scale that runs from pH0 to pH14

Alkaline describes situations where pH levels exceed 7.0.
Alkalinity is a measure of a water’s capacity to neutralize acids
The term “alkalinity” should not be confused with the term “alkaline,” which describes situations where pH levels exceed 7.0.  [15]

Chelate is a substance whose molecules can form several bonds to a single metal ion

ORP is a potential energy measured in millivolts.  When Reduction occurs the potential energy (Voltage) is reduced. 

A “reducing” agent is simply something that inhibits or slows the process of oxidation. The reducing agent does this by “donating” an electron. When we measure something’s oxidation reduction potential, it is expressed in terms of –ORP and measures the concentration of OH- ions or reducing agents. [5]

Low PH water generally has High ORP

ORP measures the presence of oxidizing or [oxidation] reducing agents by their specific electrical charge, thus Oxidation Reduction "Potential". [4]
Oxidation in simple terms is what turns an apple brown after it is cut, or causes metal to rust. [4]  This is the electrolysis and ionization of iron.
The ORP of most tap water in the USA is between +150 to +600mv, and so is an oxidizing agent. [8]
High pH ionized water demonstrates a –ORP and so is a reducing agent or “antioxidant”.

Acid (Low PH) or low potential hydrogen has a High Oxidation Reducing Potential and has potential to Oxidize other atoms, and causes metal to rust, but ionization is dependent upon a third variable called TDS (Total Dissolved Solids)..  

OK to review the above information which still gets me confused.
High ORP tends to make a Low pH, and it promotes oxidation. 

We now know that oxidation involves an exchange of electrons between two atoms. The atom that loses an electron in the process is said to be "oxidized." The one that gains an electron is said to be "reduced." In picking up that extra electron, it loses the electrical energy that makes it "hungry" for more electrons. 
Thus we get the term Oxidation (losing an electron) Reduction (gaining and electron) Potential.[16]      

When the pH is not at the proper level the plant will lose its ability to absorb some of the essential elements required for healthy growth. For all plants there is a particular pH level that will produce optimum results (see chart 1 below). This pH level will vary from plant to plant, but in general most plants prefer a slightly acid growing environment (between 5.5-6.0), although most plants can still survive in an environment with a pH of between 5.0 and 7.5. When pH rises above 6.5 some of the nutrients and micro-nutrients begin to precipitate out of solution and can stick to the walls of the reservoir and growing chambers. For example: Iron will be about half precipitated at the pH level of 7.3 and at about 8.0 there is virtually no iron left in solution at all. In order for your plants to use the nutrients they must be dissolved in the solution. Once the nutrients have precipitated out of solution your plants can no longer absorb them and will suffer deficiency and death if left uncorrected. Some nutrients will precipitate out of solution when the pH drops also. Chart 2 (below) will give you an idea of what happens to availability some of the nutrients at different pH levels:[13]

Chart 2
pH Values For Different
Hydroponic Crops
Availability Of Nutrients
Available At Different
pH Levels
(From Hydroponic Food Production
by Howard M. Resh
Woodbridge Press, 1987)

This chart is for soiless (hydroponic) gardening only and
does not apply to organic or dirt gardening.
Plant pH Range

Buffers play an important role in pH balance, as they are substances that are found in living organisms that help them maintain a certain range of pH. It is a chemical or combination of chemicals that keep the pH within its normal limits. This happens because it is able to resist a pH change by either taking up excess hydrogen ions or hydroxide ions. [11]

An example of a buffer is bicarbonate ions.  They take up extra hydrogen ions forming carbonic acid, which keeps the pH from going too low. However, if the pH gets too high, carbonic acid breaks apart to release some hydrogen ions, which brings the pH back into balance. [12]

TDS (Total Dissolved Solids) creates the pathway for the “ionization” (or more correctly electrolysis) to occur [5]as ions from the dissolved solids create the ability for water to conduct an electrical current.
The most common chemical constituents are calcium, phosphates, nitrates, sodium, potassium and chloride.
The importance of Total Dissolved Solids can not be emphasized enough. [5]

For hydroponic uses, total dissolved solids is considered one of the best indices of nutrient availability for the aquatic plants being grown, [9] but these nutrients will not be available unless the pH and ORP are also correct.

Water without mineral content or TDS, like reverse osmosis or distilled water, will not conduct the current and therefore can not be “ionized”.
Oxidation-reduction reactions are vital for biochemical reactions such as converting Ammonia (NH3+H) to Nitrite (NO2) then Nitrite (NO2) to Nitrate (NO3) through a process called fixation which makes nitrogen available to plant life.

The electron transfer system in cells, and oxidation of glucose are examples of redox reactions. [2

These three variables ORP, pH,
and TDS affect the assimilation of nutrients in plants and animals, the electron transfer system in cells, and oxidation of glucose. 

Oxidation-reduction reactions are also vital for biochemical reactions such as converting ammonia into nitrite and Nitrate.  

This is done by bacteria which prefer to live in a pH of 5.8 to 7.5. Without these bacteria  the  nutrients which plants require would become locked up with unusable salts.  

But a sufficient amount of TDS to conduct the ion exchange is also required, and each of these three components must be kept in balance.
I have not even touched upon Hard Water yet, but Hard water has a lot of buffering capacity and soft water has almost none.. 

Read more:

So understanding performance is like understanding a dance between the three variables. [5]

This topic goes even deeper:
Many essential biological chemicals are chelates. Chelates play important roles in oxygen transport and in photosynthesis. Furthermore, many biological catalysts (enzymes) are chelates.  A chelating agent is a substance whose molecules can form several bonds to a single metal ion.
Another biologically significant chelate is vitamin B-12. It is the only vitamin that contains a metal, a cobalt(II) ion bonded to a porphyrin-like chelating agent. As far as is known, it is required in the diet of all higher animals. It is not synthesized by either higher plants or animals, but only by certain bacteria and molds. These are the sources of the B-12 found in animal products. Because vitamin B-12 is not found in higher plants, vegetarians must take care to include in their diets foods or supplements that contain the vitamin.  [10]

1.  Increase the availability of nutrients.  
Chelating agents will bind the relatively insoluble iron in high pH soil and make it available to plants.
2.  Prevent mineral nutrients from forming insoluble precipitates.
The chelating agents of the metal ions will protect the chelated ions from unfavorable chemical reactions and hence increase the availability of these ions to plants.  One example is iron in high pH soil.  In high pH soil, iron will react with hydroxyl group (OH-) to form insoluble ferric hydroxide (Fe(OH)3) which is not available to plants.

Fe+3 + 3 OH- --------> Fe (OH)3
Soluble Insoluble
Chelation will prevent this reaction from happening and hence render iron available to plants.
3.  Reduce toxicity of some metal ions to plants.
Chelation in the soil may reduce the concentration of some metal ions to a non-toxic level.  This process is usually accomplished by humic acid and high-molecular-weight components of organic matter.
4.  Prevent nutrients from leaching.
Metal ions forming chelates are more stable than the free ions.  Chelation process reduces the loss of nutrients through leaching.
5.  Increase the mobility of plant nutrients.
Chelation increases the mobility of nutrients in soil.  This increased mobility enhances the uptake of these nutrients by plants.
6.  Suppress the growth of plant pathogens.
Some chelating agents may suppress the growth of plant pathogens by depriving iron and hence favor plant growth.
4. Salinity - Salinity is usually expressed in terms of its specific gravity in science labs, but in the pond and Koi world it is more common to see it as the total percent of salt in a solution.

Water Salinity Based on Percentage of Dissolved Salts
Koi function best with just ever so slight brackish water.
Fresh Water Brackish Water Saline Water Brine
< 0.05% 0.05-3.0% 3.0%-5.0% > 5%
Range in Green Perfect for Koi Ponds  0.15-0.20%
Perfect for Koi Hospital Tanks  0.25 - 0.30%
Measure Salinity Level with Easy to Use Digital Readout Meter
Measure Salinity Level with Easy to Use Digital Readout Meter

This is an excellent article which i will list again at the bottom

How does Water Hardness relate to Ionization?
Hard water has a lot of buffering capacity and soft water has almost none.

Hard water is water that has high mineral content.
The higher the mineral content or Total Dissolved Solids the higher the levels of pH and ORP. [5]
The lower the mineral content the lower levels of pH and ORP. [5]

There are two types of water hardness.  GH (General Hardness) and KH (Calcium Hardness).

Temporary hardness
(Calcium Hardness) is a type of water hardness caused by the presence of dissolved carbonate minerals (calcium carbonate and magnesium carbonate). Unlike the permanent hardness caused by sulfate and chloride compounds, this “temporary” hardness can be reduced  by the addition of lime (calcium hydroxide) through the process of lime softening. [6]

Permanent hardness
Permanent hardness
(General Hardness) is hardness (mineral content) that cannot be removed  by the addition of lime. It is usually caused by the presence of calcium and magnesium sulphates and/or chlorides in the water.  Despite the name, the hardness of the water can be removed using a water softener, or ion exchange column. [6]

Classification hardness in mg/L hardness in mmol/L hardness in dGH/°dH
Soft 0–60 0–0.60 0–3.36
Moderately hard 61–120 0.61–1.20 3.42–6.72
Hard 121–180 1.21–1.80 6.78–10.08
Very hard ≥ 181 ≥ 1.81 ≥ 10.14
Table [7]

Here is an important quote: “The presence of free (ionic) calcium at relatively high concentrations in culture water helps reduce the loss of other salts (e.g. sodium and potassium) from fish body fluids (i.e. blood). Sodium and potassium are the most important salts in fish blood and are critical for normal heart, nerve and muscle function. In low calcium water, fish can lose (leak) substantial quantities of these salts into the water.” See reference below.
Understanding Water Hardness.


Common ions

Common Cations
Common Name Formula Historic Name
Simple Cations
Aluminium Al3+
Calcium Ca2+
Copper(II) Cu2+ cupric
Hydrogen H+
Iron(II) Fe2+ ferrous
Iron(III) Fe3+ ferric
Magnesium Mg2+
Mercury(II) Hg2+ mercuric
Potassium K+ kalic
Silver Ag+
Sodium Na+ natric
Polyatomic Cations
Ammonium NH+

Oxonium H3O+ hydronium
Mercury(I) Hg2+
Common Anions
Formal Name Formula Alt. Name
Simple Anions
Chloride Cl
Fluoride F
Bromide Br
Oxide O2−
Carbonate CO2−

Hydrogen carbonate HCO
Hydroxide OH
Nitrate NO

Phosphate PO3−

Sulfate SO2−

Anions from Organic Acids
Acetate CH3COO ethanoate
Formate HCOO methanoate
Oxalate C2O2−
Cyanide CN
Table [7]

A special thanks to Dr. George B. Brooks, Jr. for corrections and this explanation of acidic effects of REDOX,

"The nitrification process does indeed acidify the water. The process takes the hydrogen from NH3+ and exchanges them with Oxygen in NO2 and NO3. (NH3 + 2 O2 => NO3- + H+ + H2O). Free protons or hydrogen is the definition of acid so the process decreases your pH. It also uses a lot of oxygen. So in your aquaponics system, oxygen in your media beds is not only critical to your roots remaining healthy but also to the keeping the bacteria alive and to mediating the nitrification reaction they do. The more O2 the better off you are (in general)."


And finally here is a site that you may find to be a handy reference

For more very good articles 
    Understanding pH, KH, GH in Home Aquariums

Wednesday, June 6, 2012

Swimming With The Fish

I hope to set up a small pool this summer.  I would like to incorporate what I've learned about water chemistry and create a natural swimming pool with plants and fish rather than chlorine or salt.

Click Here for a Slideshow of Beautiful Natural Pools

Here is one of my favorite videos

Here's a report about the added value to a home with a pool. Notice the 1000 to 2000 square foot range.
Go Figure

Sunday, June 3, 2012

Aquaponic Chemistry

I did a water test of my pond's chemistry this morning.

From left to right PH=8.0, Ammonia=0, Nitrite=0, Nitrate=0, Phosphate=5
The pond has been established for about 7 years and is pretty much care free.

It always surprises me is now low my Nitrate levels are.  It's a 1300 gallon pond containing about 70 pounds of fish which I feed 20 oz of food to every day.   The Nitrates are being consumed by about a dozed 1 gallon plants in a stream (NFT - Nutrient Film Technique).

It might be because this pond has been established for so long, but it never needs any adjustments.  I let the PH ride on the high side because it's more about being a Koi Pond, and the garden is just a benefit rather than a product.

My Other systems are relatively new, and I'm attempting to find a balance between fish and plants.  The PH buffering has been a difficult obstacle, and I may reduce the amount of rock in these systems to see if it becomes less of an influence.

My newest system is a combination of gravel bed and raft.  I'm beginning to prefer raft systems over gravel, but I like the idea of keeping a little rock in the bottom of the raft tanks.  If buffering continues to present a problem I will convert the gravel bed to a raft tank.

I plan to purchase a test kit for water hardness in order to make a better assessment of the buffering.   Ideally I would like to keep my PH at about 6.8 in order to promote iron uptake by the vegetation.

Kobus Jooste  wrote a  very good article about water chemistry last year.

Here are some more links: