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Discussion Starter · #1 ·
I’ve unfortunately neglected my aquarium for a few months due to illness - there’s only ever been plants in it, and I finally took them all out this morning so I can rescape. After digging around in the sand (BDBS), my hand was stained black and smelled of sulfur. Sooo I decided to look up exactly what went wrong for that to happen, and learned some very interesting science involving anaerobic bacteria and decaying organic matter in low-oxygen conditions.
Basically, I made a swamp. I believe the black stuff is iron sulfide-laden sludge. From Wikipedia:

As organic matter decays under low-oxygen (or hypoxic) conditions such as in swamps or dead zones of lakes and oceans, sulfate-reducing bacteria reduce various sulfates present in the water, producing hydrogen sulfide. Some of the hydrogen sulfide will react with metal ions in the water or solid to produce iron or metal sulfides, which are not water-soluble. These metal sulfides, such as iron(II) sulfide, are often black or brown, leading to the color of sludge.
I'm not exactly proud of this happening, but at least I learned something...

I plan on draining the tank and cleaning the sand as best I can, but I'd still like to reuse it if possible. Will this work? Is it dangerous for future fish?
 

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I would rinse it out very well in some buckets and it should be fine to re-use.

Worst case, buy some as it's not too expensive, but then you're stuck spending money / dealing with the old stuff / rinsing it out anyway.


I would just rinse it out very well if it were my tank.

Start up a journal so we can follow along when you set the tank back up! ;)
 

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Discussion Starter · #4 ·
I rinsed the substrate out - everything I could get out of the tank, anyway. Despite the water running clear, it still smells pretty funky. Maybe spreading it out and leaving it dry for a couple days will help?
 

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I don't think letting it dry will help. I would think just flooding back up would expose the formerly un-exposed material to oxidation, aerobic bacteria, etc., and nature would just take care of it for you. That's what I have done with past substrates. However, I must note that I have never used sand...so maybe it's just different.
 

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You could also let it sit in something that will eradicate most of the bacteria. If you want to target the anaerobes, perhaps soak it in a bucket w/ some hydrogen peroxide. Wash well after this, to get rid of the (now dead) bacteria organic matter.

My experience with re-using sand (even from a situation similar to what you described) has been good, if given a good physical wash; I blast it with the "jet" hose setting in a bucket, no more than 2 or 3 cups at a time. This way, there is a lot of sand-on-sand abrasion, which physically washes it. If I'm feeling extra cautious, I'll put it all in a bucket, drain as much water as possible, then pour in some white vinegar and let it sit a few days. Rinse it well before using (vinegar is 5% acetic acid, which has low toxicity to fauna and flora, so rinsing well will suffice). Also, when setting it back up, I'll put 1/3 of the sand in, then squeeze the sponge from a good healthy tank filter into it, to "seed" beneficial bacteria. Then the rest of the sand goes in, and plant heavily (plant roots will transport some oxygen into the substrate layer). HTH.
 
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