Wood is one of those things we kind of take for granted in aquascaping.
A lot of thought will typically go into the selection and placement of wood in our scopes. There are probably as many different opinions on which wood is best as there are aquascapers who use it.
However, one thing that we don't see a lot is discussions on how wood "behaves" upon submersion, and what to expect from different types of wood when used underwater. Now, I don't claim to be the world's leading authority on using wood for aquascaping, but I do have some experience working with the stuff...and a pretty good feel for how terrestrial materials interact with the aquatic environment.
First off, this is not going to be a piece on how to choose the best piece of wood for your next aquascape, nor a review of available wood for aquascaping. Rather, it will be a discussion on what happens when we place wood in water...
First off, let's think about where our wood comes from.. It doesn't take much to figure out that the most important thing is that the wood must be…well, DRY! It can’t be “live”, or have any greenwood or sap present, as these may have toxic affects on fishes when submerged. Sap can be toxic, even when dry, so if you see a piece of wood- even dry- that’s displaying some sap- it might be a good idea to take a pass. In our experience, it’s a better idea to purchase your wood from sources known to offer “aquarium safe” wood, and not worry about suitability, toxic concerns, etc.
For the sake of this discussion, let's just assume that you're working with wood that's been properly collected and is suitable for aquarium use.
When you first submerge wood, a lot of the dirt from the atmosphere and surrounding environment comes off, along with tannins, lignin, and all sorts of other stuff from the exterior surfaces and all of those nooks and crannies that we love so much. And of course, there are the tannins. Now, I don't know about you, but I'm always amused (it's not that hard, actually) by the frantic posts on aquarium message boards from hobbyists that their water is turning brown after adding a piece of driftwood. I mean- what's the big deal? Oh, yeah, not everyone like it...I forgot.
The reality, as you probably have surmised, is that driftwood will continue to leach tannins pretty much for as long as it's submerged. As a "tinter", I see this as a great advantage in helping establish and maintain the blackwater look, and to impart the humic substances that have been proven to be very beneficial to the health of almost all freshwater fishes. It's a unique aesthetic, too.
What I'm more concerned about are the impurities- the trapped dirt and such contained within the wood. As you probably know, that's also why I'm a staunch advocate of the overly conservative boil and soak approach to the preparation of botanicals as well. A lot of material gets bound up in the dermal layer of the tree where the wood comes from. The bulk of the dry mass of the xylem (the "network" within the tree which transports water and soluble mineral nutrients from the roots throughout the plant, and comprises what we know as "wood.") is cellulose, a polysaccharide, and most of the remainder is lignin, which is a sort of complex polymer.
Why the botany lesson? Well, because when you have some idea of what you're putting into your tank, you'll better understand why it behaves the way it does when submerged! In a given piece of driftwood, there is going to be some material bound up in these structures, and it will be released (gradually or otherwise) into the water that surrounds it, with a big "burst" happening on initial submersion. This is why, during the first couple of weeks after you submerge wood, that the water often becomes dark and even cloudy. There is a lot of "stuff" in there!
It's far better, in my opinion, to take the time to start the "curing" process in a separate container apart from the display aquarium. This is not rocket science, nor some wisdom only the enlightened aquarists attain. It's common sense, and a practice we all need to simply view as necessary with terrestrial materials like wood and botanicals. You may love the tannins as much as I do, but trust me, your tank could do without the polyscaccharides and other impurities from the outer layers of the wood. The potential affects on water quality are significant!
It's pretty plain to see that at least part of the reason we see a burst of new algae growth and biofilm in wood recently added to an aquarium is that there is so much stuff bound up in it. Algal and fungal sports can literally "bloom" during the initial period after submersion, and this alone is great reason to take the long, slow approach to wood prep. In fact, I've long made it personal practice to submerge wood which I intend to use in my tank a couple of months before I set up my tank. This will enable a good percentage of the bound-up contaminants and unwanted organic materials to be released before the wood ever graces your aquascape! And it goes the wood a chance to saturate and sink, too!
Boiling? Well, sure, boiling can hasten the process somewhat. The biggest problem is that most of us don't have a kettle or other large enough container in which to boil a big old piece of wood, so the long-term "pre-soak" is the optimal approach.
And let's face it, even with preparation, when you combine water, light, and organics, you're likely to get some algae and biofilms for some period of time. Some algae and biofilms are to be expected in the earliest days of "submersion. These tenacious life forms will exploit available nutrients and conditions that are appropriate for their survival. I remember deliberately NOT pre-soaking the wood in my office tank (I love torturing myself, apparently) just to see how nasty this could be. (oh, the things I do for you in the interest of sharing knowledge!)
It literally took about 4-5 months before the wood stopped producing biofilm and attracting hair algae.
Eventually, the familiar "patina" of harder algae came to prominence. And minor biofilm on the softer parts of the wood will still pop up on occasion...Just like it does in nature.
And of course, along the way, you can incorporate some "biological helpers", like algal and detritivorous-consuming fishes (I used Spotted Headstanders, Chilodus punctuatus, 'cause I'm a characin kind of guy...) and even snails (yikes!) to help out.
If you recall my article on my quest for "blackwater-compatible livebearers" a couple of days back, the idea of keeping some for a continuous "assist" in algal and biofilm "management" in a blackwater tank is what prompted me...
And of course, good old-fashioned aquarium husbandry and stepped-up maintenance practices never hurt, either!
And having a good, soft-bristled toothbrush on hand can help with the "day-to-day" upkeep, if needed.
Obviously, happy endings typically will happen with aquarium wood, given the passage of time and perhaps a bit of assistance from the fish geek, but it's important to understand WHY the algae and biofilms appear on wood, and how to react when they happen. Like so many things in a truly "natural" aquarium, they may not meet our aesthetic standards, but if we have a greater understanding of just what they are, who they appear, and how to address them (or not..), we can make that mental shift that you hear me ranting about so often on these pages.
Embracing a new paradigm of what a "natural" aquarium really is. One that doesn't cause us to rush off, headless, screaming into the night (or onto Facebook) when some algae or biofilm appears! Goes with the territory.
In the end, wood use has been, and likely always will be a part of aquascaping practice in aquariums. And with a bit of understanding about some of the stuff you can expect- and why it occurs, you'll not only develop a better appreciation for your beautiful finished product- you'll develop better personal practices and protocols for handling wood in the future. You might even learn to love the amazing things that happen when wood meets water!
Until next time.
Stay patient. Stay observant. Stay calm.
And stay wet!