Actual effects of carbon on pH

[easaquatics]

I have tried different carbon filter media from different manufacturers and would like to share what I have found so far and receive some feedback and experiences from other people who use carbon filtration.

I use 3liters of carbon in a large bag filter. I use a Beckman Phi 350 pH meter that is calibrated daily using a 3-point calibration (4, 7, 10.01)

The first carbon used was Kent's Reef Carbon (Manufacturers description: Removes organic pollutants, stains, and entrained toxic gases in marine and freshwater aquariums or ponds. Contains the finest pelletized activated bituminous coal based carbon. Pore size is in the 20 to 2,000 Angstrom range, ideally suited for removal of large organic molecules. Super activated with very high iodine and molasses numbers. Less than .2% ash making it suitable for sensitive species such as discus. Will not leach phosphates or promote undesirable algae growth, suited to sensitive reef systems! Engineered for water flow, will not clog easily like small granular or pelleted carbons. Out performs any carbon especially coconut shell!)

What I found: after thoroughly rinsing the carbon with RO water (pH 6.5), I found that in my 200+ gallon flow through system, the pH was immediately raised from 7.4 to 9.3, my monitors began to alarm within seconds.
Kent Reef Carbon Trial #2: after thoroughly rinsing the carbon with RO water (pH 6.5), I soaked it in RO for 24hrs, and found that the soak water was at pH 10.0, I rinsed again and soaked for another 24hrs and found that the pH dropped to 9.3, I repeated this process and found that it took at least 5 days to reach an acceptable pH of 7.8.
This has been confirmed by no less than 3 more trials.

So now I have purchased some Seachem Matrix Carbon (Manufacturers description: a truly unique activated carbon. It is formed as a spherical bead for optimum hydrodynamics, and will not pack. It permits maximum water flow and contact with its high density of macroporous binding sites. MatrixCarbon™ has a very low ash content as indicated by its minimal impact on pH. Even when added to distilled water, it does not raise pH above 7.0.While all carbons contain phosphate, regardless of false claims to the contrary, MatrixCarbon™ has the lowest detectable leachable phosphate content of all major carbon brands tested. MatrixCarbon™ outperforms other high grade carbons by at least two-fold when compared for total capacity to remove aquarium organic matter, rate of adsorption, and duration of use.) I have conducted the same sort of tests and this is what I have found:
After thoroughly rinsing the carbon with RO water (pH 6.5), I soaked it in RO for 24hrs, and found that the soak water was at pH 8.0. This is a full unit higher than is claimed by Seachem. I plan to do this test over and again and will update this thread. I rinsed again and soaked for another 24hrs and found that the pH dropped to 7.8. I rinsed again and soaked for another 24hrs and found that the pH dropped to 7.4; finally an acceptable reading because I keep the system at 7.4.

So the next question is, what is the basis for claims like: outperforms other high grade carbons by at least two-fold , and 1 L will EASILY treat 1600L for several months (when nutrient and waste loads are so highly variable)?

I have read and been told that acid washed carbons are the best to limit effect on pH, others say to simply rinse and soak for as much as a month. I would appreciate reading any thoughts and experiences that other people have had.

[easaquatics]

BUMP!

Nobody has any info to add?

Is Seachem Tech support really afraid to touch this?? What gives?

[Tech Support LK]

Sorry for the extremely delayed response. This post was
somehow overlooked.
Through extensive research and testing done here before
product release, we have seen no evidence of carbon having
any such impact on pH even when used in excessive
quantity. In light of your findings, we decided to
experiment using our Matrix Carbon and de-ionized water.
You did not state what quantity of Matrix Carbon you used
in your experiment and in what quantity of water, so we
performed the experiment using 3 different quantities.
Based on "250 mL will easily treat 400 liters for several
months", which is what we state on the bottle, we
performed our experiment using 10 times, 54.5 times, and
95.5 times this amount. This is what we found:

Using 1 Liter of de-ionized water (tested with calibrated
pH probe) with pH=6.42, we placed the water in a glass
beaker with a magnetic stir bar. After washing the Matrix
Carbon with de-ionized water through filter paper, we then
added 6 mL of Matrix Carbon to the 1 L of water. This
quantity is 10 times the suggested amount on the product
label.
1st stabilization with pH probe, pH=6.34.
2nd stabilization, pH=6.39.

We then proceeded to add 30 mL more of Matrix Carbon for a
total of 36 mL in one liter of water (54.5 times the
suggested amount).
1st stable pH reading, pH=6.53.
2nd stable pH reading, pH=6.60
3rd stable pH reading, pH=6.67

After waiting for 5 minutes the pH remained at 6.67.

We then added 27 mL more of Matrix Carbon bringing us to
about 95.5 times the suggested amount.
1st stable pH reading, pH=6.73
2nd stable pH reading, pH=6.80
3rd stable pH reading, pH=6.84

These results only reinforce our statement that "Even when
added to distilled water, it will not raise pH above 7.0",
as it clearly did not. Even when used in an excess of
almost 100-fold, the pH still remained under 7.0. It is
obvious, and we do not deny, that any activated carbon
will tend to raise pH to varying degrees. However, you can
see from these results that when our Matrix Carbon is used
in suggested quantities and even in excess, there is
minimal impact on pH. You also must consider the fact that
when you add carbon to your tank, this usually a well
buffered system. If excessive amounts of carbon are added
to de-ionized water (which is completely devoid of any
buffer) and exhibit such minute impact on pH, you should
see little, if any, impact on well buffered water (i.e.:
your tank) with the addition of Matrix Carbon. In addition
to this, in an aquarium, organic acids are being produced
which help to negate pH increases.

As far as our product being superior to others has a lot
to do with the porosity of the material along with other
characteristics. Our carbon is micro-porous and macro-porous
allowing for better removal capacity. Ours also has the
lowest amount of leachable phosphate on the market. The
spherical shape of Matrix Carbon allows for optimal water
contact, thus allowing it to remove as much as possible
form the water. The specs of the product are listed on the
website. Unfortunately, I do not think Kent or any other
company lists any of this information on their activated
carbon or else we could compare numbers for you.