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Re: Aquatic Plants Digest V2 #597


>Subject: Freshwater Plants and Brackish Water Conditions

>        I have set up a 10 gal. plant tank with several species
>of plants, including: Hygrophila polysperma, Cardamine lyrata,
>some specimens of dwarf and narrow Sagittaria, as well as some
>Java fern (Microsorium pteropus).  The plan is to make this the
>new home for a small group of Bumblebee gobies (Brachygobius
>xanthozona) that I have my eye on.  The dilemma is that these
>fish seem to be living quite happily in a tank where the
>salinity of the water is around 20-22 ppt (a specific gravity
>of approx. 1.014 to 1.016).  After a little experimentation, I
>found that this means I'll be adding approx. 3-4 tablespoons
>of salt (non-iodide table salt) per gallon of tapwater to bring
>the salinity of my tankwater within the above range.

That does seem on the high side for freshwater aquatic plants, although
some are undoubtedly more tolerant of salinity than others.  (I don't know
which ones are.)  Since my priorities put plants first and fish second, the
question occurs to me, Do the bumblebee gobies really need that much salt?
Could they get along with less, perhaps one tablespoon per two gallons?

>Subject: Apon Bulbs
>In a retail shop yesterday I saw "Apon Bulbs $.49".  So I bought one.  It
>has begun sprouting.  How do I plant it?

Plant it partly buried in the gravel with the top part, where the leaves
are coming out, still visible.  It can also be held down with a pebble or
>There isn't, I don't suppose, any way to tell what variety it is from bulb
>shape, is there?

Some Aponogeton species can be distinguished by bulb shape. A. ulvaceous
has big round ones.  A. madagascariensis has long ones about 1/2 in thick
that can sometimes branch.  A. rigidifolius has even longer and thinner
ones.  They aren't really bulbs, but are rhizomes (underground stems).  A
bulb stores food in fleshy leaves.  An onion is an example of a bulb.

>Subject: Re: Alternanthere sessilis

>I'm a little surprised. I've always seen Sunset Hygro sold as Hygro poly var.
>"Sunset", and always assumed it was a hygro. I've grown it for years side by
>side my Hyro poly and they grow almost identically. Now I know it's really
>Alternanthera sessilis. I was planning on ordering some A. sessilis, glad I
>didn't! Well, anyway, it grows fine submersed in both my indoor
>CO2/PMDD/Metal Halide setup, and my no-CO2 outdoor tank, where the leaves are
>much smaller and quite red, maybe due to natural light. I have seen it go
>emersed occasionally, and it does seem to require a bit more light than Hygro
>poly to do well.
More likely, the dealer mislabeled the plant, and it was really A.
sessilis.  Sunset Hygrophila is just like regular, green Hygrophila, except
that it has white veins and a greater tendency to produce a red-orange
color, especially on the newer leaves.  A. sessilis is dark beet-red, and I
don't know of any variety of Hygrophila that has that color.

>Subject:a CO2 Q or 2.
 Is CO2 injection necessary in a brightly-lit tank?
>That is, necessary in terms of allowing the plants to have enough CO2 to
>keep up with the rate of photosynthesis being demanded by bright lighting,
>to prevent pH swings large enough to be harmful to fish etc.  Can I simply
>create good current to allow CO2 easier diffusion?

It depends on what kinds of plants you are trying to grow.  There is a wide
range in the abilities of aquatic plants to extract CO2 from water.  The
majority of aquarium plants are unable to get CO2 except as free, dissolved
CO2 in the water.  A smaller number can also take up the bicarbonate ion,
HCO3-, and extract CO2 from it leaving behind the hydroxide ion.  They have
a distinct advantage over the others who can't utilize bicarbonate when
both are together in a well-lit location with a limited supply of CO2.
Plants in this latter group are often found growing in shallow ponds with a
lot of plants and very little flow-through.  Plants in the former group are
usually found in rivers and streams where the ratio of water volume to
plant volume is very high, and the CO2 content of the water is considerably
higher than in the crowded ponds.

If you have a tank that gets sun, and the plants get the pH up to 8.0 or
higher, you should stay with plants like Vallisneria, Sagitteria,
Ceratophyllum, Eigeria (Elodea), Najas, and Echinodorus.  Even in this
group there will be differences in ability to get CO2.  I suspect that
Eigeria and Najas could win out over Echinodorus, for example.  Hygrophila
is a good indicator plant.  If it doesn't grow in this tank, then don't
even think about trying any of the Crypts.  In general, plants that grow
well emersed, but can also grow submersed will need higher CO2 levels than
those which are more fully adapted to submersed growth.

If you have a well-lit tank with plants that can extract bicarbonate, you
should check the pH now and then, because some of these plants can extract
CO2 so efficiently as to get the pH over 9, and this level of alkalinity
can be hard on fish.  I once had a tank with Eigeria (Elodea) densa and
Zebras, and one day I  noticed that the fish were not eating well and that
they were swimming weakly.  I measured a pH of 9.6, and the fish recovered
their normal behavior and appetite when I lowered the pH with additional

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174
In Jackson, Mississippi with sunny, pleasant spring weather.