Pool filter sand gone black (pics)

[DonMD]

I'm tearing down my 125 show tank because I got tired of the 3-D background, and because I need space for all the juvies I've grown from the proven pair I bought from Hans. My tank had pool filter sand for about 3 years. About a year and a half ago, or even longer, I began noticing during water changes, that some of the sand being disturbed was quite black, not the tan color it was when I put it in.

I have done weekly water changes, and at least every two weeks have aggressively vacuumed the sand. Even so, on one side of the tank I got all this black sand under the top layer. Has anyone else had this issue? It's curious. Didn't cause any problems with the fish.

http://i484.photobucket.com/albums/rr204/dellenberger/IMG_2370_zpsf443999a.jpg
http://i484.photobucket.com/albums/rr204/dellenberger/IMG_2369_zps5855c54c.jpg
http://i484.photobucket.com/albums/rr204/dellenberger/IMG_2368_zps324855ca.jpg
http://i484.photobucket.com/albums/rr204/dellenberger/IMG_2367_zpsf3be6404.jpg

[lipadj46]

That's just what happens with sand, even pool filter sand. It goes anaerobic under the surface layer. Stinks right?

[Discusdude7]

Yeah this happened too me before as well

[Tazalanche]

I had just assumed it was from the Seachem Flourish fertilizer tabs we used before swapping to MiracleGro fertilizer stakes.

[discuspaul]

It could very well be caused, in the main anyway, by the disintegrated fert tabs over the years. Possibly anaerobic gas pockets as well. And last but not least, sand like any other material, loses out (wears out) to time and usage in various ways -exposure to light, accumulation of various wastes and detritus, etc.
I've avoided such a problem by continuously siphoning out some decent percentage of the sand every couple of months & replacing it with new - as well as doing a complete replacement of substrate with new sand every 2 or 3 years. Has worked for me - but I nonetheless continue to find a few black patches in the planted areas where the root tabs have been placed.

[DonMD]

Very interesting responses, thank you. I did not ever put any fertilizer tabs in this substrate, since I never had plants there, so we can rule that out. And curiously, no, it never stank, although I agree that it looks like it could be from anaerobic bacteria. But I often sand the python in that section and stirred up the sand. Perhaps I was overfeeding. Anyway I've taken all the sand out and am redesigning the tank. It's always good to know that other hobbyists have experienced similar issues that one finds. Thanks for your responses!

[joanstone]

That's just what happens with sand, even pool filter sand. It goes anaerobic under the surface layer. Stinks right?

+1

[Chicago Discus]

It's from the 3d background dropping off small particles and mixing with the sand........Josie

[joanstone]

I've had that happen in varying degrees many times. You especially see that in a saltwater tank with a deep sand bed. I've had sand stored in buckets before and that's exactly how it turns out. It's what Don said.