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isoetes ferns


I've had a couple little clumps of an isoetes sp. (probably lacustris) for
some time.  The plants appear healthy but they grow *very* slowly.  The
quills are about 4 inches long and curve back to the substrate.  The
plants put on new quills at about the rate necessary to replace the quills
that they lose from time to time.  It would be a real nice ground cover if
it grew a little faster.  Their space is being taken over by other
plants and I need to do something about it. Does anyone know how to
get better growth out of isoetes?

The plants are in a 20 gallon tank with 40 watts of fluorescent light.
Substrate is 5+ years old and contains two sizes of gravel plus peat and
potting soil. Its been a very successful substrate.  The isoetes are
housed with Crypt. wendtii, Heteranthera zosterifolia, Bacopa caroliniana,
Fontinalis moss, Egeria densa, duckweed, E. tenellus and some recently
added lilaeopsis (sp?).  I moved a couple of my Barclaya seedlings into
this tank, but those aren't really a threat to the isoetes;  the tenellus
on the other hand are a menace.  There's also some sort of hair algae
that's grown into the surface of the substrate and that used to cause the
isoetes some problems, but the algae is now mostly under control.

The taller plants partially shade the isoetes, but it isn't obvious that
shading is a real problem for it.

The tank gets DIY CO2 (isoetes take CO2 in through their roots) and the pH
is about 7.4.  The water is soft and well buffered out of the tap but
supplemented to 1 degree of magnesium hardness and 5-10 ppm potassium.  No
other fertilizer is added regularly.

Oh yeah, fish.  There's a false SAE and a couple otos plus an
undertermined number of swordtails of various levels of maturity.  It's a
moderate load.

Your input would be appreciated.

Roger Miller
On the high desert.