A  P  R  I  L     2  0  0  1 1 5 W  A  T  E  R     Q  U  A  L  I  T  Y media in the rest of the system. Pre-filter
‘hole’ size is measured in microns, the
smaller the micron rating - the smaller
the ‘hole’. See Figure 4.
     Figures  3  and  4  show  choice  is
relatively simple for hardware and pre-
filters. But when you start investigating
purification  media  performance,  it
is trickier.
     There are many different purification
media available on the market, probably
the most readily available media are
activated carbons.
ACTIVATED CARBONS Activated carbons vary enormously in
quality and performance.  They can be
‘very good’ or ‘extremely poor’.  With
activated carbons it is a case of ‘you get
what you pay for’.  As a specialist said to
me about an extremely cheap activated
carbon in circulation, ‘the best you
can say  about  it  is  that  it’s  black
and granular’.
     Activated carbons come in powder,
block and granular forms. Activated
carbon blocks are made from powdered
carbon held together with resin based
adhesive. This resin acts like a barrier
and prevents water contact with some of
the carbon, thus reducing the effective
media life. Because of this, the filtration
industry   sees   carbon   blocks   as
having  short  sprint  performance;
granular carbons are chosen for longer
staying power.
     The majority of activated carbon
cartridges   sold   in   the   UK   are
manufactured in America for domestic
and commercial use. Ratings are based
on warm water testing for free chlorine
reduction and do not allow for the
effects of chloramine and colder water.
Ratings are shown in US gallons which
are smaller than UK gallons (1 US
gallon = 0.83 UK gallons).   
Ratings shown in Figure 6 seem rather impressive. However they are
theoretical projections, used historically to
determine how much water activated
carbons may treat, for the reduction of free
chlorine. Theoretical projections are fine if
they take into account all parameters
affecting medium life. Projections in Figure
6 ignore the presence of chloramine, cold
water and larger UK gallons.   
       The amounts and percentage mix of
total chlorine and chloramine as shown in
Figure 7 are not abnormal in UK tap
water. It is therefore not possible to
determine chloramine reduction using a
single, simple mathematical equation based
on free chlorine test results, because of the
variables involved.
     Pulling the above information together,
Figure 8 demonstrates the dangers linked
to projecting the effective life of activated
carbon using free chlorine and warm water
testing when planning to treat UK tap
water for fish protection.
     When reading laboratory test results it is
important to understand that each test
result is accepted to be correct within
certain tolerances. The accepted tolerance
allowed for Figure 8 test results is + or -
5%. Bearing this in mind:
     In Figure 8, the first sample was taken
after the purifier had treated 42 UK gallons
of UK tap water. The second sample was
taken from the same purifier after it had
treated a further 777 gallons of water.
     The first and second sample’s test
results support each other. Although only
•   Vessel strength varies - use pricing as      a guide.
•   Pressure release valves - allow the
     bleeding off of airlocks. Cheap vessels
     don't have these valves.
•   Connectors - BSP threads determine
     plumbing. 1/2in outlets are preferable.  
•   Vessel Life - strongest vessels are
opaque e.g. some blue, have a five
year, lifespan. Clear plastic degrades
faster and clear vessels usually have
a recommended life of one year.
VESSEL MYTH: ”You can only tell if a cartridge is blocking
by looking at it through a clear vessel.”
Not so! For a start you can’t see inside a
cartridge! As cartridges block or airlocks
occur, water flow slows. Bleed vessel
using the pressure release valve. If water
passage speeds up, the problem is
resolved. If water flow remains slow,
replace the blocked pre-filter/cartridge.
Caution! Clear vessels must be kept in
the dark. Sunlight encourages algae
growth within the vessel, which speeds
up the blocking of the cartridge.
VESSELS: ‘Cheap’ Isn’t Always Best PRE-FILTER MYTH. ”The smaller the holes (micron value) in a pre-filter - the better.” Micron ratings differ depending on the pre-filter's job e.g.: for industrial ‘large particle’
entrapment, use 60+ micron. For bacterial entrapment, use below 0.5 micron to about
0.2 micron.  
•  10 or 5 micron pre-filters should be quite adequate for koi use when treating tap
and using granular purification media
•  1 micron pre-filters are often used to protect carbon blocks. They are known as
     ‘polishing’ pre-filters and can block too rapidly, especially if they are unprotected
     by pre-filters with a larger micron rating.  
•  The smaller the micron rating - the more expensive the pre-filter becomes.
1,000 microns = 1 millimetre Projected amount of free chlorine Theoretical amount of warm water an in testing water, no chloramine present activated carbon block cartridge may treat 2.0 mg/l 3,000 US gallons 1.0 mg/l 6,000 US gallons 0.5 mg/l 12,000 US gallons 0.25 mg/l 24,000 US gallons Cartridge size approximately 10in height x 2.5in diameter Total chlorine Free chlorine content Chloramine content 0.07 mg/l 0.01 mg/l 0.06 mg/l 0.30 mg/l 0.05 mg/l 0.25 mg/l 0.50 mg/l 0.45 mg/l 0.05 mg/l 0.84 mg/l 0.43 mg/l                                                                                           0.41 mg/l

  The percentage mix of free chlorine and chloramine is extremely   variable. Low values
  of total
chlorine can contain a high percentage of   chloramine and high values of total
  chlorine can
contain   a small percentage of chloramine.
Total chlorine is a mixture of free chlorine and chloramine. Thus chloramine can be
determined by subtracting the free chlorine result from the total chlorine value. When
chloramine is not reported in a Drinking Water Report, if ammonium (or ammonia) is
present assume that chloramine is in the tap water supply.  
  Ammonium + free chlorine form chloramine
Free chlorine + chloramine form total chlorine
Figure 7 illustrates the variability of the free chlorine/chloramine mix found in UK tap water.
Chloramine is intended to remain in water for far longer than free chlorine and is therefore
more difficult to reduce.