Re: metals left in petrified wood
Although I am not currently active due to a lack of extra space, (lapidary equipment and rocks) I have set up both fresh and salt water tanks with all self-collected rocks as decor elements that cost me only the time to gather the rocks and which fetched a lot of nice compliments from other aquarium keepers.
Some texts on aquarium keeping and aquarium shop personnel warn against introducing garden variety rocks as decorative elements in tanks, maintaining there is a danger of minerals from them which may be toxic to the fish dissolving in the water, or adversely altering the hardness or pH of the water. I am inclined to suspect this advice from the aquarium shops, as many have a pony of their own in the race in the form of rather exorbitantly priced gravels and slate and other natural and artificial rocks they want to sell you that are "guaranteed safe". Due to my own experience to the contrary, I also suspect the book authors are simply dutifully parroting a caveat from the body of lore preceding their work rather than speaking with the voice of experience on the topic,
I have not found this to be an issue with ordinary rocks - the sort of stuff you might collect from a river or stream bed, or find exposed at or near the surface in an outcrop. The reason for this is those sorts of rocks have already been exposed to the elements including water for a great deal of time, so any highly soluble minerals that may have been in them when they formed have already been removed by natural processes. Another factor to consider is that if you are practicing proper aquarium maintenance, you will be doing frequent partial water replacements to help rid your tank of nitrite/nitrate and ammonia build up from the bacterial breakdown of detritus and uneaten food, which will also have the effect of continuously diluting and carrying off whatever water soluble minerals your decor rocks might be sourcing.
I wouldn't worry too much about adverse effects from petrified wood. Some aquarium texts advocate a prophylactic coating of epoxy resin on self-collected rocks, but this seems overkill to me and I am inclined to be more concerned about the potential adverse effects from toxins in the epoxy than I am from the rocks.
I think the primary danger posed by decorating aquariums with garden variety rocks is not one of toxic minerals, but rather the potential introduction of harmful bacteria or other organisms carried in on the rocks. So it's not a bad idea to first thoroughly clean the rocks with a scrub brush and soapy water, and then give them a final rinse in boiling water.
This all said, you do need to keep in mind that water is an amazing solvent. Given enough time and exposure water will even dissolve silica, which is how your petrified wood came to be replaced with rock in the first place. And it is at least possible, although not very probable, that you could inadvertently incorporate a toxic rock if you just pick up your decor rocks at random. If you are much experienced at aquarium keeping, you probably have set up one or more isolation tanks where you quarantine new arrivals for a period of time before introducing them to a large, established community tank. If you want to be extra cautious about the rocks you are introducing, you could do the same with them, employing particularly sensitive invertebrates in the quarantine tank as miner's canaries.
Have fun decorating your aquarium, and keep on rock'n!
From Bob Keller - October 25, 2007 at 09:15:45