Originally Posted by Byron
There are many types of "fungus" and I can assure you all that some of them are deadly. I did not imagine what happened in my tank, solely from white fungus that appeared on a new piece of Mopani Wood after about 2-3 days. Nor did the other aquarist I met in a local fish store who had the same issue and his corys all died within a few days of fungus appearing on a new piece of Mopani driftwood. Plus Dawn has had similar experiences. This is not made up stuff folks.
Fungus that appears on a bit of uneaten flake food is another matter entirely. As is fungus that appears on open wounds on a fish or other aquatic vertebrate. I am not a microbiologist so I don't know how many types of fungus there may be. Some may be safe, some clearly are not. Dawn may be able to offer us more on this. But please do not write this off as some sort of make-believe. There is a definite and real danger with some types of fungus, and it kills fish.
Byron is correct. There is no way to pinpoint the exact species of fungus growing on a given piece of aquarium wood (unless you want to spend months working with the Smithsonian Institute sorting it out). What we do know is that fungus growing on anything in an aquarium housing fish poses some risk to the animals, whether directly visible or not.
Try to think of it this way... a person out in the woods searching for berries, finds something they don't recognize... do they eat it or leave it? Should they risk the potential for getting sick, possibly dying from eating something toxic? To me this falls into the category of "just because you can doesn't mean you should."
There are a number of species of fungus that are not directly toxic to the animals, but rather feed on or utilize something within the water chemistry, something the fish/animals need to survive. In some cases this can be oxygen, some cases could be specific minerals. Fungus doesn't grow if conditions are not perfect for it, but has the ability to lie dormant for years, awaiting just the right situation to allow it to thrive. There are fungus spores in the air we breathe, all around us, and even inside of wood. Baking wood can trigger the growth of some species of fungus, as can boiling it, because its a matter of temperature that sets the right environment for it to start.
I have been keeping wood in my aquariums for over 20 yrs. Very few pieces have ever given me a fungus issue. When working at the store we had wood in over 100 tanks, and again, very seldom a fungus issue. Of all my fish keeping friends and colleagues over the course of 20+ yrs, fungus on wood is not "common" in most types of wood, and we tend to avoid those few types where it is. Why? Because we know the dangers to our animals, the risk involved.
And one last comment about identification... unless you're going to put the fungus under a microscope and do the work do properly identify it as fungus, algae, cyano bacteria, etc. there is no way to know positively if it is safe or not. For those who claim its common and "no big deal" I would have to say you are very lucky, but luck is known, at some point, to run out. I hope for your sakes that it doesn't run out at a critical moment and kill your fish.
The best thing to do with wood that is growing fungus that doesn't go away with a good scrubbing in some clean water, is to throw it out, find another use for it, or take it back where you bought it from and ask them to replace it for a healthy piece. Knowing that certain types of wood are well known for it means either taking the risk of wasting your money or avoiding those types of wood.