Reverse Osmosis & How I Use It
by Don Zilliox
First published in Some Things Fishy, Newsletter of the Tropical Fish Club of Erie
County
Aquarticles
"What is osmosis? It is the phenomenon of water flow through a semi permeable
membrane that blocks the transport of salts or other solutes through it. Osmosis is a
fundamental effect in all biological systems. It is applied to water purification and
desalination, waste material treatment, and many other chemical and biochemical laboratory
and industrial processes."
"When two water (or other solvent) volumes are separated by a semi permeable
membrane, water will flow from the side of low solute concentration, to the side of high
solute concentration. The flow may be stopped, or even reversed by applying external
pressure on the side of higher concentration. In such a case the phenomenon is called
reverse osmosis."
I hope you kind of get the idea of just what Reverse Osmosis (RO) is from those two
small paragraphs taken off the Internet. All I am interested in is getting very pure water
in which I can able my apistogrammas to breed and raise their fry. Now the first problem
is that the fish are not able to exist in "pure" RO water that has a 0 ppm
(parts per million) of TDS (total dissolved solids). There are chemicals available on the
market today at your LFS (local fish store) that you can add to the RO water to bring back
some of the ingredients necessary for your fish. But they cost money and sometimes you
need lots of it; not just the 4oz container priced at $6.95.
First what size RO unit is needed? Ask yourself the question, "How many tanks am I
going to use it in and how large are they?" In my case I use it in about 10 tanks
with a capacity of around 100 gallons. I decided to purchase a 25-gallon per day (gpd)
portable unit for about $125.00. I'm lazy so I don't change water every day and I figure
50 gallon every other day is more than I'll need for those few tanks. I set it up in the
basement on a small table and provided two barrels; one of 35 gallons and the other 55
gallons. Testing my tap water I found it to be 175 ppm and 0 ppm from the RO hose and 190
ppm in the so-called "waste" water barrel. I assume the missing the other 160
ppms were being trapped in the 3 membranes on the unit. In my opinion, 190 ppm is not that
bad for most South American cichlids in which to live and grow. I didn't purchase an RO
unit until about 6 years ago and had no problem raising or breeding some Apistogramma
species before then. As a matter of fact, most will breed in water with about 80 ppm TDS.
So instead of trying to add chemicals and adjusting pH I just mix some RO water with
"waste" water to attain whatever ppm I think is necessary. The rest of the
"waste" water is used in my grow-out tanks. My pH is normally 7.5 but the RO
unit does bring it down to somewhere around 6.5, which seems to be fine. This way I don't
have to constantly be adding something for any adjustment. One more thing I do for really
difficult soft water fish is add a little common garden peat moss. I toss about 2 big
handfuls of peat in a 5 or 7-gallon pail and fill with the RO water. This usually brings
the pH down to around 5.5 and adds that tea color everyone talks about. Some people boil
the peat so it will sink faster but I am in no hurry so I let it float for a week out two
and then it siphon through a brine shrimp net. I also believe that boiling may extract
some of the beneficial ingredients you are looking for. There is also a liquid product
available from Tetra that includes peat extract. (Costs money too.)
I've seen too many messages on the Internet where new fish keepers want to adjust their
water to simulate conditions in the wild. If you just want them for beautiful community
tank, don't get excited about changing your water. I'm positive your LFS is not displaying
them in anything but your local tap water and I'm sure they look great in those tanks.
Even for breeding purposes I wouldn't change the water right away as maybe the fish were
bred in your own backyard and the fish are getting used to local water. I know many of my
friends who are breeding Discus in our regular medium hardness water with much success.
All I can say is don't get too excited about water conditions unless you are using hard
"well" water. Even then, I know non-breeders who are keeping their fish in
excellent condition. I purchased my RO unit from Wet Thumb Aquatics in Michigan but they
do not stock them any more, so I now buy replacement membranes directly from the
manufacturer, SpectraPure. I recently got a new pH meter ($29.95) and TDS ($19.95) tester
from Hanna Instruments.
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