Cyanobacteria, doxycycline and azolla

[kyle at onebox_com]

Hi everyone,

I'm starting to get a cyanobacteria outbreak in my 10gal, moderate 
to heavily planted tank  So far it is mostly on the
 roots of the floating Ceratopteris in my tank but I'm sure it will
 probably spread soon.  Having seen that erythromycin is the common
 cure I have a couple questions.

I have a bunch of leftover Doxycyclene tablets from my trips to
 Southeast Asia (its a Malaria preventative among other things). 
 Since it is an antibiotic I assume it will kill cyanobacteria. 
 However I don't know if it has any particular affect on fish.  Does
 anyone have experience with this?  For the time being I took out
 the ceratopteris and put it in a bowl with some doxycyclene, but if
 the outbreak spreads it will get onto planted plants and hardware
 that I can't easily separate from the tank so I may have to do
 something to the tank itself soon.  

On this note, I have some Azolla fern in my tank (yes, I actually
 like it and duckweed, I'm a botanist!).  I've gotten to wondering if
the fact that it has symbiotic cyanobacteria in its cells could 
contribute to cyanobacteria outbreaks (e.g. the leaf gets damaged or
 the plant dies and the cyanobacteria heads out on its own).  Anyone
 have knowledge about this (hard data's great but I'll take
 anecdotes too!)?  If people think Azolla could contribute to
 outbreaks then I'll probably get rid of it.


-- 
Kyle Williams
kyle at onebox_com - email
(707) 583-2064 x2092 - voicemail/fax