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Kenny Song's problem tank
I'm inclined to agree with other suggestions regarding the probable
cause of Ken's fish dying, and that large water changes (while one
possible explanation) is NOT the most likely cause of the affliction. I
suspect that he may be dealing with bacterial and fungal infections
which are the result of other deteriorating water conditions. The
subject is only peripherally related to aquatic plants so I'm going to
concentrate my answer on the plant related aspects. (substrate, what did
you think? ;-)
Ranked in order of probability:
1) rotting driftwood (easy to check; take it out, smell it)
2) substrate problem
3) bacterial/viral pathogens
4) toxins in the tap water
Since moving the fish to another aquarium seems to save them, I'm
inclined to discount 4) and possibly 3).
The use of driftwood or wood as a decoration in planted aquariums is
peripheral to aquatic plants in much the same way as discussing mending
tanks or discussing the breeding and maintenance of popular fish
commonly used in aquariums especially for algae control. Anyhow wood is
not my subject and I'm cautious when using it so I'll leave that for
somebody else.
Ken mentioned using a layer of laterite covered with gravel and since
he's from Malaysia, I'm wondering if this is lateritic soil which he
collected himself? Ken, have you used this substrate material
successfully in other planted tanks?
Sometimes a particular mineral soil might contain some soluble minerals,
especially alkaline ones, which we need to think about when collecting
soil. I suggest putting a soil sample in a container of water and
checking for pH reactions. That will help detect carbonate salts. I
doubt that's Ken's problem if he selected a red, well leached clay soil
of volcanic origins which might be prevalent in Malaysia and the
Indonesian archipelago (including the Philippines). Sometimes an
alkaline soil in an arid region like a desert or an alkaline bog also
accumulates other soluble metal salts like copper, mercury and lead so
that's why the pH test gives another clue since those soils are likely
to be basic (i.e. not acidic).
So here are the precautions I suggest:
1) know a little about your soil. You can refer to the links on my web
page for more information about soil horizons etc. Soil taken from a
well drained, forested or meadow location is a good choice. Go for a
hilly spot.
2) submerge the soil for a while and then change the water. You can do
this before you install it in the tank. This also helps to stabilize
organic soil components which will undergo biological decomposition most
rapidly for 3-4 weeks. I don't install fish into a new soil tank right
away. I usually add an expendable test fish first such as a Platy (they
breed like mad, oops! off topic ;-) a few days after the tank is
planted. I also perform a couple of 90% water changes before putting the
fish in for a few days. That may be over cautious but I figure the water
is cheap. Never be in a rush, eh?
3) a soil with some humic material will sorb dissolved metal ions which
might cause micro nutrient toxicity. That is one of the reasons that I
use peat (Canadian Sphagnum Peat Moss), mixed in a thin layer in my
substrates. Peat is not quite as stable biologically as soil humus but
its close especially after a few months under water.
Diana Walstad did some experiments using soils and subsoils. She
hypothesized that micro nutrient toxicity was a problem with the use of
subsoil. This is covered in one of the TAG back issues. Check the TAG
back issue subject index if you're curious. I'm don't think that Diana's
experiment was conclusive in _proving_ that subsoil is categorically
bad; in fact other soil scientists suggest that subsoil is a preferable
source of micro nutrients. It is extremely unlikely that a well leached
tropical soil is going to contain much in the way of soluble metal salts
but then if you collected it from the back yard of a chrome or nickel
plating factory, you might have contamination. Pesticides herbicides,
fertilizers, oil and chemical spills are other possible contaminants.
Lead leaching from house paint is another possibility that has been
mentioned.
I don't know how common micronutrient toxicity is when using soils in
substrates. Usually we only hear about the success stories. If anyone is
interested in experiments in this direction, please contact myself or
Paul Krombholz.
Another reason I like peat is that it releases humins into the water.
These are low grade toxins which inhibit the growth of bacteria and
fungi. You need to know if the fish you keep prefer high or low levels
of humins in their water. South American catfish, neons, discus and
Anabantoids (Gouramis and Bettas) all prefer water with humins (so
called black-water). Of course, tap water is not supposed to contain
humins...
So long as the tap water is fit for drinking and doesn't contain an
excess of chlorine or chloramine, I don't consider large, frequent water
changes to be a problem. They are, in fact, very beneficial because they
remove excess nutrients and low grade toxins from your tank water.
If you are adding calcium carbonate to boost Ca content and as a pH
buffer, you normally add this with the water change. The pH buffers
already present in your tank water will dominate the pH even if your tap
water is like rain water so pH fluctuations should not be too much of a
concern. Of course everyone keeping fish should have a pH test kit and
be familiar with any pH problems with their tap water.
Fish are far more affected by bad water conditions than plants.
Steve (opinions expressed are my own)