Calcium
Reactor Substrate -- Phosphate Levels by
Greg Hiller
Sponsored in part by:
In
an endeavor to save a few dollars in this very expensive hobby, several
years back I tested some alternative
calcium reactor substrates1 to determine their elemental
profiles using an analytical technique known as inductively coupled
plasma.Prior to my work, Craig Bingman also tested some calcium
reactor substrates2 in a similar fashion.In
a nutshell, from a phosphorus standpoint Dr. Bingman’s experiments
suggested that Super Calc Gold (which from what I can tell is no longer
commercially available) had about twice the concentration of phosphate
as Koralith (sometimes also called Hydro-Carbonate). In my experiments I
found that a locally quarried limestone had phosphate levels several
fold higher than Koralith, but still about 40% lower than a crushed
coral aragonite that I'd been using in my calcium reactors at the time.
Since
the time of my experiments, a new calcium reactor substrate called ARM
(aragonite reactor media) has been marketed by CaribSea.CaribSea was recently claiming in advertisements in some of the
aquarium literature3 that according to testing conducted by
an independent lab, the phosphate content of ARM was less than 1/500th
of that in Koralith medium.As folks in the sciences know, exceptional claims demand
exceptional experimental proof.I was a bit skeptical to say the least.In looking at ARM even with the naked eye, it is clear that it is
made up of pulverized corals, clam and snail shells, and other naturally
occurring calcium carbonate materials of marine origin, and like all
such materials significant quantities of phosphate would have to be
present as they are in all life forms.
Testing
methodology:
1.A 10 gram sample of each calcium reactor substrate was dissolved
in concentrated lab grade hydrochloric acid in about 300 ml of DI water.
I used 25 ml concentrated hydrochloric acid, which was a slight excess.
2.The samples were neutralized back to a pH of about 7.9 with 5
molar sodium hydroxide (took about 24 ml).
3.Samples were then diluted to a total of 1 liter with DI water.
4.The resulting solutions were allowed to settle for a few moments,
and then samples were taken and run on the Hach phosphate test kit
(model PO-19).To get into the range of the Hach test kit (0-50 mg/l) it was
necessary for me to further dilute the sample from my locally quarried
limestone.
5.As a secondary test, I further diluted all the samples by 10X and
ran the Hach calcium test kit (model HA-4P) to see if the same amount of
calcium was being generated by the dissolution of the substrates, and to
allow a calculation of a Ca/PO4 ratio for each substrate.
Results:
A.ARM Reactor Substrate:
The
phosphate in the ARM reactor medium sample (received from Champion
Lighting) tested out to 2.0 ppm.ARM calcium came out at 385 ppm, or 3850 ppm (when accounting for
dilution).Therefore, the calcium to phosphate (Ca/PO4) ratio for
ARM was 1925 (high numbers are best).
B.Koralith Reactor Substrate:
Koralith
medium (received from Champion Lighting) came out at 2.8 ppm. Koralith
calcium tested out at 385 ppm, or 3850 ppm (when accounting for
dilution). Therefore, the Ca/PO4
ratio for Koralith was 1375. Koralith therefore has 40% higher phosphate
levels than ARM.
C.Locally collect limestone:
My
locally collected limestone (Conklin Limestone Quarry, Lincoln, RI) came
out at 6 ppm. The calcium level came out a bit low at 300 ppm, or 3000
ppm (when accounting for dilution).It is possible that this sample was not completely dissolved,
which would therefore affect the phosphate number, but not the Ca/PO4.The Ca/PO4 ratio for the limestone was 500.
D.Reagent Controls:
A
control of 25 ml concentrated hydrochloric acid neutralized with the
sodium hydroxide and diluted as the other samples came up very low, but
detectable using the Hach phosphate test kit, and the background had no
effect over the numbers above.Because
no calcium carbonate sample was dissolved in the processing of this
sample, considerably more sodium hydroxide was needed to get the pH into
the sampling range.
Conclusions
and Discussion:
As
shown in the table, the phosphate level of ARM calcium reactor substrate
is almost 30% lower than the level in Koralith, but certainly no where
near the 1/500th number claimed by the manufacturer.The phosphate levels in the Conklin limestone are considerably
higher, but still within a range that in my opinion makes it useable,
and, since I have been using the Conklin limestone for about the past 2
years, I know it is usable!
Substrate
Phosphate
level (ppm)
Ca/PO4
ratio (high numbers are best)
ARM
from Carib Sea
2.0
1925
Koralith
2.8
1375
Conklin
Limestone
>6.0
500
How
important is the level of phosphate in your calcium
reactor substrate?Well, the details of that answer go well beyond
the scope of this article, but have been discussed in
detail in the reefkeeping
literature.14,15Suffice to say that significant quantities of
phosphate are added to our tanks by simply feeding the
fish.High
levels of phosphate are thought to promote algae
growth, and in some cases may inhibit normal
calcification in corals.14Because of this, any methods or procedures that
limit the introduction of additional phosphate into a
reef tank seem prudent.If you really think your corals and critter are
growing so fast that they are limited by low
levels of phosphate, it’s very easy to reach for
that can of flake food!
Other
Notes:
The
ARM medium appears to have a lot of shells in it. I
have no idea what the trace nutrient profile looks
like for this material. Unlike the other substrates
that were tested, when dissolving the ARM medium,
there was quite a lot of brown foam formed.I was careful to collapse this foam back down
into the solution before taking samples for the
analysis.
Before
I performed the experiments in the lab, I did some
quick and dirty measurements at home in my sink with
some hardware store quality hydrochloric acid (also
called Muriatic acid) and a Pinpoint pH probe. The
sodium hydroxide I used was lab grade, but I would
conjecture that one might be able to purchase sodium
hydroxide from the hardware store of sufficient grade
to make some home experimentation possible.Anyhow, my quick and dirty experiments at home
yielded similar numbers, but there was a bit more
background from the reagents.I would reason that if one just wanted to
directly compare head to head any particular calcium
reactor substrates for phosphate levels one could do
it at home with hardware quality reagents.Please be very careful if you try this, the
acids and bases use in these experiments are VERY
potent, and capable of burning through skin and
clothing, and some of the fumes given off could easily
make one very sick.
