NetMax wrote:

Thanks for sharing the pics.
Thanks so much to you for the answers!

Your wood does not appear to have been dried.

Those pieces of wood were chopped by my father off the trees at least 2
years ago, and were intended to be used as firewood. I boiled them for
almost 1 hour and let the dry a couple of days before putting them in the
tank. I'm saying that not to disprove your theory, but in the hope that
whatever sap, humic acid, and other organic matters are being released,
there isn't much left in the wood.
Now I have to decide what to do. Taking the wood off is the most obvious
choice, but it implies a mayor change to the tank set-up, which is rather
difficult in its current location. Considering that the wood wasn't
completely "green", I'd like to know your opinion on the following course
of action:
1) add activated carbon to the filter, to remove as much organic matter as
possible
2) do large (30% - 50%) weekly water changes
3) dim the light
All this waiting for the plants to grow enough to starve the algae of any
nutrients.

your Neons must be tasting the effect in the water, and might
start becoming affected.

any particular symptoms I should be watching for?

Thanks again,

FP