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-8- TBAS September 2018 ....................
15 to 50 ppm, although some species may tolerate somewhat higher hardness.
Neon tetras require very soft water of 15 to 30 ppm in hardness and a slightly
acid pH of 5.0 to 6.5.
Dwarf cichlids of some species will require water of 10 to 30 ppm in total
hardness with a pH of 5.5 to 6.5.
Discus require water very low in ionic strength and a hardness of 20 to 40
ppm, and a pH between 5.0 and 6.5. It has been the experience of this author
that we are able to get a sufficient percentage of fertilized eggs in hard alkaline
water; but the eggs do not survive to hatching as they are rapidly attacked by
bacteria and then fungi. It is possible. that the egg membrane is weakened due to
the high osmotic gradient across it in the presence of dissolved salts in the water.
The membrane, thus weakened, is then more susceptible to bacterial attack.

Marine Application

Recently the reverse osmosis process is being used in make-up water
for marine systems. A properly designed reverse osmosis unit will remove 99%
copper which has to be removed for invertebrates and will also remove 99% of
phosphate, polyphosphate and nitrate from make-up water.
It will remove 98% of silica acid (Si0 ) which has been implicated in golden
2
diatom blooms. Therefore reverse osmosis is the best process for removing
excessive nutrients from make-up water when the desire is to eliminate microalgae.

Medical Application

The reverse osmosis process has been used quite extensively for kidney
patients. Reverse osmosis will remove 96% of sodium in tap water.

Conclusion

As we all know, due to heavy industrial and waste problems, the water
quality in the world today is not like it was many, many years ago and is gradually
getting worse. With the introduction of reverse osmosis to the aquarium trade it is
now possible to breed species of fish which were once considered hard to keep
alive. It is by far the simplest method of desalination available to the aquarist.

References
1. Jenkins, David and Snoeyink, Vernon, Water Chemistry, John Wiley & Sons,
1980; Fig 4-17, p 164.

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