[AGA Member] Blue-green algae

["Wendy S. Katz" <katzndogs@alltel.net>]

I have several medium-tech tanks in which fish and plants are thriving. (a
55 gallon, a 20G high and a 10 gallon).  They were set up with 50% Flourite
or 100% Eco-complete substrate and are fed with Flourish Excel and Flourish.
Lighting is from 4 T12 sunlight bulbs each on the 55 and 20 and two T8
sunlight bulbs on the 10. All had a slight transient BG algae bloom during
the break-in period that went away on its own. I also have a 5 gallon cube
that has no substrate and only window illumination, from a SW-facing window
shaded by a large oak tree.  Java moss, Java fern and Mayaca grow
luxuriantly in it, fertilized mainly by a few guppies and their food (every
couple of weeks or so I give it a drop of Flourish).

Not long after reading Diana Walstad's book, I acquired another 20 gallon
high and decided to set it up as a no-tech tank, since my 5-gallon is doing
so well.  I used a fine sand sold for children's sand boxes, rich Kentucky
clay soil that has not seen chemical fertilizer in at least 8 years,
probably longer,  a layer of boiled peat atop the soil, topped off with
sand.  The tank sits in a NE-facing window, and has one T8 sunlight bulb.
It is populated with 6 male guppies, 4 German Rams, 4 adult Glow light
tetras plus 3 juveniles, and 3 Otocinclus. The water is treated with
homemade peat extract to maintain pH around 6.8.
Nitrates are below the limit of detection and all the fish appear to be in
excellent health.

The plants and sand in this tank have a heavy growth of blue green algae
that won't give up.  I tried doing several large water changes a couple of
days apart, vacuuming out most of the BG algae each time...it grows right
back.  Now it's moving onto the walls and getting heavier.

I'm ready to resort to antibiotic.  If I use Erythromycin, what is the best
timing of water changes to allow the drug to work but prevent toxins
released from dying cells from harming the fish?  How long should I continue
treatment?

If you were to change one condition to prevent a recurrence, would you favor
increasing the illumination, providing carbon, or...?

Sorry this got so long, but I tried to anticipate questions.  Thanks!


-- 
Wendy S. Katz
Lexington, KY
mailto:katzndogs@alltel.net

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