Many
killifish species live in very pure water. That is it contains few
minerals. As a result, they are adapted to this water. With mineral
laden water such as found in a lake, or water obtained form a well
in a limestone substrate, the “hardness” is greatly
increased due to dissolving the surrounding minerals and concentrating
the mineral content by evaporation. Most Aphyosemions and
many of the South American annuals will survive nicely in hard water,
but may not be able to fertilize eggs. It is my understanding that
the egg membrane quickly hardens once the egg enters the water and
the sperm cannot penetrate the hardened membrane. This is probably
much simplified, but for water treatment purposes is close enough.
There are three methods of removing minerals from water. Distillation,
mixed bed ion exchange, and reverse osmosis (RO). A home water softener
does not remove minerals. It replaces calcium ions with sodium ions.
Same for the little water softening “pillows” sold in
aquarium shops. I will not say these are of no use, however when
I used them they did not help much. Distilled water is not cheap,
but is available commercially. This is Distilled, not bottled spring
or drinking water.
To distill water it must be converted to steam and then the steam
condensed. Costs $ to boil water!
This leaves us with two alternatives; mixed bed ion exchange columns,
or a reverse osmosis unit. A mixed bed is a once thru system. It
cannot be recharged in the home. The two resins must be separated
and rinsed; One in hydrochloric acid and the other in caustic soda
for regeneration. The columns can be purchased at many local aquarium
shops and are not a bad deal if you wish to treat a small amount
of water. A new column costs around $20. It will treat about 100
gal of water depending on the mineral concentration of the water.
If you have 2 to 5 five gallon tanks, this may be the most cost
effective way to go. All the water entering the unit is demineralized
and no water is wasted. Additionally, if you have low water pressure
(less than about 50 psi) the alternative RO unit may require a pump
to boost pressure to function with decent efficiency.
 For
a larger supply of water (assuming sufficient water pressure that
the purchase of a pump ($175) is not required), a reverse osmosis
unit is probably more cost effective. A RO unit capable of producing
between 20 and 80 gallons of demineralized water every 24 hours
costs about $120. This includes a “three stage” unit.
The first two stages are a sediment filter and a charcoal filter.
These prevent clogging and destruction of the RO membrane, which
is the third stage. Units come with a garden hose fitting on the
inlet and two 1/8 inch nylon tubes on the outlet. One tube is the
water passing through the membrane; the second is from behind the
membrane and server to prevent build up of minerals and sediment
on the inlet side of the RO membrane. This “constant flush”
is about 4 to 5 times the water volume as that which is demineralized
and exiting the other nylon tube. The water is of excellent quality
on both sides of the membrane since it has all passed through the
filter and carbon filter. The “flush” water has about
20% higher mineral content than the water supply line. Fine for
most uses.
It is not possible to easily “re introduce” this water
to the house water supply since it is at a lower pressure than the
house water supply (it went through the filters resulting in a pressure
drop) and a high pressure pump would be needed. Now, that's about
$120. There are a few accessories that, although not essential,
are very desirable and worth the money.
First, it would be nice to shut off the RO water before the RO reservoir
overflows. (As a low cost reservoir, a 30 gal Rubbermaid garbage
can serves the purpose quite well.) A small float valve (available
from RO unit dealers at a cost of about $15) can be used to shut
off the supply to the Rubbermaid garbage can. This does not shut
off the rinse water though, but if sent to a drain, at least will
not flood the fish room. An alternative at a cost of $80 is an electronic
shut off that will turn off the water supply when the reservoir
is filled. More up front, but a water bill savings if you are forgetful
like me.
Another nicety is for the RO unit to come with clear filter canisters.
Nice, but a better solution is a small pressure gage (about $15)
to monitor the pressure on the RO membrane. As the pressure drops
due to need for a filter change, flow through the RO membrane decreases.
Simply changing filters when you think it is time can be costly
as the sediment filter plus the carbon block filter costs about
$30 to replace.
There is no problem replacing them; just buying the new cartridges
can run up the cost if done needlessly. Again just put out the $15
and be happy you did. This is actually cheaper than see-thru cartridge
holders and more useful.
A small test meter to determine the conductivity of the RO water
is most useful. There are meters calibrated in microseimens (one
microseimens is one micro MHO, which is the inverse of resistance
in micro ohms) and meters calibrated in parts per million Total
Dissolved Solids (TDS) They both measure the inverse of the resistance
(conductivity) of the water to electrical current. Pure water is
not a good conductor; it is the dissolved minerals in the form of
ions that carry the current. Thus a measure of the resistance of
the water can provide a measure of the mineral content. A standard
is used to set the calibration of the meter if extremely accurate
results are desired. For aquarium measurements, the setting on the
as received meter is more than adequate.
The RO water is far too pure for fish. They do need a mineral content.
Additionally, with no mineral content pH swings are not prevented
(no mineral buffering present). In the wild, water of near 1 ppm
mineral content can be the habitat of many of our killifish. The
pH does not swing since the water is constantly being changed (killi
means stream, remember) and there is no buildup of waste products.
To put some mineral content back into the RO water to bring the
TDS up to a reasonable value (most killies do fine at 40 to 150
ppm depending on species) you can re-mix some of the waste water
into the RO reservoir or, like I do, buy some chemical buffer like
“RO Right,” a Kent product. I have no affiliation with
them, but I have found the RO systems offered by Spectrapure and
Kent to be competitive in price and reliable. A search for Spectrapure
on the web will provide a website with additional information on
RO unit function, supplies and ordering information. |
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