When decorating my tanks I have gone many routes when it came to rocks. Most recently I had the idea that if I got the rocks from underwater in a local stream everything should be “kosher”. I tested the water first in the stream and everything seemed great so I carefully selected rocks which were free of any algae or other things of this nature. I brought the rocks home and vigorously scrubbed them with a stiff nylon brush in de-chlorinated water. I put them in the tank and all was good for a day or so…then came the water from hell. No mater what I did, I could not keep fish alive in the water (btw I use my own previously quarantined healthy feeder fish when starting new tanks or doing anything that could possibly endanger a more expensive and/or fragile fish). All the water tests were perfect; it seemed some sort of pollutant was in the rocks. The rocks looked so pretty in the tank, but I finally gave in and just removed the rocks because without fish, it’s just a big expensive bowl of rocks and water!
I should have known I was going to have problems when there were no signs of life in the stream I got the rocks from, but I am stubborn and (and a bit dense from time to time) so I just kept telling myself it was because it was winter and the water was just barely above freezing (I am in Burke, VA, about 20 minutes from the Pentagon, and all of this occurred about a month ago). I eventually had to tear the tank all the way down because even after the rocks had been removed there were still issues with weird algae, along with other problems. As of only about a week ago, the tank is FINALLY up and running with no issues at all and all inhabitants are very healthy.
On a prior occasion when I used rocks from outside I went the exact opposite way. At the time I was not the most knowledgeable of aquarists and so I simply went out into my back by a large drainage ditch and collected some large rocks. Most of you who know your stuff are probably cringing at this moment, as I am, just thinking about my stupidity. I did at least have a touch of sense, and rinsed the rocks with a high power washer as they were kind of muddy. I then put them in a clean empty tank and began cycling. Everything was great for about two weeks then what looked like small dried water spots formed on the inside of the glass – under the water! I was a bit flabbergasted and at the time the only thing I knew to do was to do water changes. I was a bit more energetic back then and kept up with daily 30% water changes for the better part of two weeks. The spots eventually went away and not one fish was lost in the process! The tank in question is actually still up and running and is crystal clear with all inhabitants doing great – rocks and all.
All of that to say: just be careful. Even the best of intentions can end in disaster. But, as I have illustrated, sometimes you just get lucky, as I did in the second scenario. I planning in the next month or so to go to a much larger stream/river to collect some rocks and try again. This time though I will not only wash the rocks, but I also plan to boil them a few times. Then first add only rocks and water and let those run for two weeks to make sure all is good, then and only then will I add fish. I will be happy to share my results if anyone is interested. Also, just for reference, neither of the tanks in the above illustrations contained live plants, just fish, rocks, and water – at the time no substrate. The second tank, which is still running, never got substrate as it is perfectly healthy without it and I liked the look so much I just left it alone.
Sorry for the dissertation, it’s just my style. Hope this helps someone…