>To survive or breed? Does anyone have any accurate data on the lower pH
>limits that rainbowfish will successfully spawn and develop at? I certainly
>know folks who have had rainbows not reproducing, checked their pH, found it
>acidic, raised it and gotten eggs shortly after. Unfortunately few people
>keep good enough records to really know for sure.
I think anyone who has kept rainbowfishes for any length of time would know
that pH certainly does has some effect on their breeding and generally
health. So convinced was I that I monitored all my aquariums (31) every week
for a period of around 6 months. The reason I didn't reply to this email
earlier was that I have been looking for the results which I have lost
somewhere? Perhaps it was on my hard drive that someone on this list, whom I
wont mentioned, accidentally erased :-)
The ironic thing is that many people comment on the effects of pH without
ever monitoring their tanks. Below and above certain pH levels rainbowfishes
will be adversely effected. Their slime coat can reduce, making them more
susceptible to disease. Their fecundity definitely drops and, ultimately,
the gas exchange in the gill membranes will be so reduced that the fish may
suffocate. Just what that pH range is I'm still not sure but I have had them
die at levels below 5.0
The other thing is that there is a BIG difference between natural conditions
and aquarium conditions - they are just not the same. Even in the wild if
you bother to check the water where you collected them from and then go 100
m upstream and 100 m downstream you will get an entirely different value.
The fish have the ability to seek better conditions or the conditions are
not stable long enough to have any serious effect. However, its a different
story when it comes to aquariums where the whole aquarium is the same pH and
the fish do not have any option to move anywhere else.
My weekly monitoring definitely showed that there are _wild swings_ when it
comes to aquarium water. Even between morning and night time. If the
aquarium water is not well buffered any acid that is added or develops will
drive down the pH. Consequently, the daily pH swings can combine with
longer-term acid accumulations in well-established tanks and cause the pH to
suddenly drop with catastrophic results for the fish. From my own
experience, I found ALL my rainbowfishes looked healthier, bred more and
just looked overall in better condition when their water was maintained
above 7.0 and I routinely adjusted their water accordingly. I always
adjusted the alkalinity rather than the pH itself as I found this was a less
stressful result for them. I used a KH generator powder manufactured by
Aquasonics (Australian) for marine tanks.
However, having said all that rainbowfishes seem to survive reasonably well
in waters with a pH between 6 and 9. At values below 4 or above 10, they
will normally die, but as I said above I have seen them die at levels below
5.0. When the survivors were remove to another tank with elevated pH levels
they improved.
In well-buffered aquariums with alkalinity levels above 50 ppm (mg/L), the
pH will be more stable. In the morning, carbon dioxide levels are high and
pH is low because of respiration during the night (carbon dioxide forms a
mild acid when dissolved in water). When a suitable light source is
provided, algae and other aquatic plants will produce carbohydrates and
oxygen from carbon dioxide and water by photosynthesis. As carbon dioxide is
removed from the water, its pH increases. In aquarium systems, the pH will
generally drop in relation to the fish load, biological filtration, feeding,
and maintenance schedules. Therefore, the pH in an aquarium system is
biologically different from that found in nature.
You also have to take into account the population of a given aquarium and in
my case my tanks were what most would consider as slightly over crowded :-)
In less populated tanks the pH doesn't swing as much. However, do yourselves
and your fishes a favour by keeping them above 7.0 - but not too high :-)
As a last word - Peter is correct when he assumes that not many people
maintain accurate records or for any length on time. I even got 3 different
values of the same water by using 3 different methods ie. using bromothymol
blue, phenol red, and a properly calibrated pH meter. The colorimetric
method can suffer from interferences due to discoloured water samples,
salinity, organic matter, and substances, which can oxidise or reduce the
reagents. In water with very low alkalinity, the indicators themselves may
actually alter the pH of the sample. As for pH meters you should always
remove a sample of water from the aquarium to measure the pH. Measurement by
immersing the electrode directly in the tank can be severely compromised by
other undetectable electrical currents from power filters, heaters, etc.
Also, pH electrodes which are not routinely cleaned and standardised will
not provide accurate readings and will be no better than, and often far
worse than, a colorimetric measurement made with standard aquarium test kits.
Adrian.
Adrian R. Tappin
Brisbane, Australia.
"Home of the Rainbowfish"
http://www.ecn.net.au/~atappin/home.htm