As you get deeper into the world of marine
aquariums, you quickly realize that the happiness of your organisms depends on
the quality of their water. You might be tempted to pour tap water into your
aquarium, since it’s convenient and cheap. But, depending on whether your water
comes from a municipal source or from a well in the back yard, it can have too
high of a pH, as well as harboring heavy metals, chlorine and other chemicals
less than savory to your prize aquarium inhabitants. The answer to your water
problems lies in owning your own reverse osmosis (RO) unit.
RO units purify the water by forcing tap water through
a series of membranes and filters. The membrane lets the water molecules move
through, but larger molecules, such as limestone and other minerals, and
contaminants are stopped by the membrane. The end result is water that is up to
99 percent pure, depending on the type of membrane used.
The most basic membrane is a cellulose tri-acetate
(CTA) membrane, which is manufactured from organic materials. Using a CTA will
purify your water from 88 to 94 percent, but this membrane does not remove
chlorine from the water. You’ll still have to have a dechlorinator for your
aquarium, or you can set your water out for 24 hours before using it in order
to let the chlorine gas dissipate.
A more advanced membrane is the thin film composite
(TFC) membrane. Made of synthetic material, the TFC membrane in your reverse
osmosis unit will remove 97.5 to 99 percent of water impurities.
Another membrane consisting of synthetic material is
the high removal membrane. Like the TFC membrane, the high removal membrane
purifies your water from 97.5 to 99 percent, with the added benefit of also
removing silicates.
Along with the membrane, the RO unit also comes with
a carbon block, a sediment filter, and deionization (DI) resin, if it is a four
stage unit. If the RO device you’re looking to buy has less than four stages, it
means the DI stage was left out. The DI resin is another method of purifying
your tap water by means of an ion exchange. An RO unit without a DI stage can
purify your water to 98 percent. A DI stage added to your RO unit purifies your
water up to 99.9 percent. Sometimes all you need is 98 percent pure liquid, but
if your fish are really finicky, the extra 1.9 percent purity provided by the
addition of a DI stage can mean a great deal to your aquarium success.
Once installed, the maintenance of a reverse osmosis
unit is reasonably simple. If your tap water comes from a city municipal source
and is loaded with chlorine, a good rule of thumb is to change out the carbon
and sediment portions of the RO unit about every six months. The membrane in
your unit often lasts for years. However, the membrane can clog with time or
even develop holes. The best way to monitor your unit is with a total dissolved
solids (TDS) meter, which lets you keep track of the quality of your RO
operations. For example, the DI resin should read between 0 and 1 using a TDS
meter. If the resin reads above 1, it should be replaced.
Do Not Use
Pure Reverse Osmosis Water
A reverse osmosis unit does a fantastic job
purifying your tap water for aquarium use, but it can create a product that’s
actually too pure for your saltwater livestock, by stripping essential minerals
from the water. One way to avoid this problem is to mix some of the tap water
back into the RO water. Or you can add store bought minerals to the water. Even
with a good RO unit, you still need to test frequently for pH and mineral
levels, and water quality.
Reverse osmosis water is available by the gallon at
supermarkets and aquarium stores. The point that makes owning your own RO unit
worthwhile is that you control the quality of the water, since you can monitor
your own unit. Purchasing water from the store means you have no idea when the
RO unit last saw maintenance.
