Tropical Fish Keeping - Aquarium fish care and resources

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pretzelsz 06-05-2010 06:44 PM

Stupid rock question
I want to add some rocks from my yard(some dug up from garden beds) to my aquarium. I want to know how to make tank safe. I have seen the don't boil rocks thread but it only really explains not to heat them. I will pour vinegar on them to check but i dont have anything else to do stuff with. please tell me how to make them safe.

Byron 06-05-2010 07:50 PM

With any item from outside, there is always a risk. Boiling rocks is a no-no because they will explode. Scrubbing them under very hot water (straight from the tap) with a stiff brush will remove dirt and (hopefully) bacteria and such stuff. But it is what may be inside that is the unknown.

If the rock has been exposed to chemicals (fertilizers, lawn weed stuff, gasoline, oil) it will (probably) have absorbed some, and this could once underwater slowly leech out over time and poison the fish. I have used rocks from streams, etc., long ago, and I understood (though not as clearly as now) that I was taking a chance. That decision has to be yours.

The acid test is to determine the calcareous state of the rock; calcareous rocks will slowly dissolve minerals (calcium and magnesium primarily) into the water, raising hardness and pH. That is no problem in livebearers or rift lake cichlid tanks, but is not good for soft acidic water fish, especially if your tap water might be slightly basic/alkaline to start with. Vinegar is often suggested, but it is too weak an acid; the acid in the regent #2 of the nitrate test kit is stronger and a drop of two will be sufficient; if it fizzes the rock is calcareous.


pretzelsz 06-05-2010 08:45 PM

I did the test and nothing happened. My tank has 5 swordtails and 5 danios(20 gallon tank) I will wash them more and it is a risk yes and if they did leak in the tank(which is also planted) would the thing that could possibly be in it be not harmful if i did weekly changes of 20%? it is a very established tank running for 3 years. So I think I might take the chance and if it does go wrong I will be sad because I have raised all the swordtails from fry(from original fish) but I would have a better home for my Betta(after cleaned) or my new SW quarantine but i think the rocks are okay just granite type rocks.

Are granite type rocks okay?

iamntbatman 06-06-2010 05:12 AM

Granite is usually fairly inert so will be alright in a fish tank, again with the caveat that any "found" rocks might contain pesticides or other chemicals that could leech out into your tank.

pretzelsz 06-06-2010 09:57 AM

I know that the stuff can leak out and I don't want my fish to die but they have been sitting there getting rained on and such with no human interactions for years(moved here no one lived here for a long time) and they are right next to a swamp and we don't use and chemicals because they aren't "green" . Also how long would it be before the chemical leeched into the tank? like immediately, slowly releasing it over the time of like a year(small rocks but not pebbles), in years, days. what?

Byron 06-06-2010 11:52 AM

You are asking a question that none of us can fully answer.

First, rain or washing is not going to cause toxic substances to leech out (if any are present to begin with) like being submerged will; the same holds for wood. Once these items are permanently under water, the water will penetrate the rock or wood, depending (in the case of rock) upon the composition as some rock is more porous than other rock. Granite is fairly dense, but I'm not a geologist so I can't say to what extent. As the water penetrates the rock, it can pick up toxic substances and draw them out, so to speak.

But again, without knowing the total history of the rock in question, we have no way of knowing what if any substances it may have absorbed over its history exposed in the yard.

Water changes are not always sufficient to dilute such toxins, depending what they are and in what strength. Let me give you a personal example of the problem I had from a piece of wood. I bought it in a fish store, so I expected it was OK. I had a lot of wood in my 115g tank. After several months, during which I did 50% water changes weekly (I still do this), I noticed the fish were getting lethargic, esp the Corydoras [they are highly susceptible to toxins and frequently are the first to show signs of something being wrong]; they sat on leaves respirating very heavily but slowly. New fish put into the tank died within a couple days. I tested for everything imaginable, nothing. Finally I was referred to the Freshwater Fishes Curator at the Vancouver Aquarium, and we started exploring possible causes. The second cause he considered was something toxic in the wood. I removed all of it, did a 75% water change, and the response from the fish was amazing. By the end of a week though they began to show symptoms again. He surmised that whatever was in one (or more) pieces of the wood had probably slowly leeched into the tank and adhered to the gravel, plant leaves, filter media, rocks, etc. I pulled the tank completely apart, washed the gravel in buckets of very hot water, washed the plant leaves, replaced the filter media, scrubbed the rocks. Put it all back together, and no problems thereafter. Something toxic in the wood had obviously slowly leeched out and been absorbed elsewhere. It can take years for this to manifest itself. It is now some 15 years after that catastrophe, I have the same gravel and the same rocks, all new wood; it has never returned.


pretzelsz 06-06-2010 12:38 PM

okay thank you Byron. I will keep an eye on my tank after putting it in and if that does happen I will scrub everything in the tank and replace the gravel/sand with most likely all sand since i have alot of left over sand. And if it does happen I know what caused it and know how to fix it so I hopefully don't have a huge problem.

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