# Sand turning black, should I worry?



## Niki7

In my 20 gal tank, I set up the substrate via the beaslbob method - peat, sand, gravel. The play sand was a light tan color when I put it in. Now, there are bands of black within the sand layer in a couple places. It is too far down I think for it to be settling in the sand but maybe it is. I have heard of anaerobic bacteria spots and I am worried this is what the black spots are. Any ideas? Should I worry or no?


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## Big Dog

Can you post some pictures of what it looks like?


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## beaslbob

Could be some of the peat got in the sand layer.


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## Gizmo

Depending on how long the tank has been set up, the black veins could be nitrifying bacteria setting up shop in less-dense pockets of your sand.

If it is anaerobic bacteria, just mix the sand layer lightly to evict them from their homes.


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## Scuff

If it were a pocket of gas, it would look like a pocket of gas, as stupid as that sounds. Typically discoloration of the sand below the top layer is simply algae growing between the glass and the sand. I wouldn't be too worried to be honest.


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## Niki7

Here is what it looks like:

The peat got mixed in on the far right, I can see that spot...but these are the greyish spots under the black rock that I am concerned about. Tank has been going less than a month.


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## Alasse

They are anaerobic bacteria spots...or heading that way...if you disturb them they stink

I had some appear in my 1st sand substrate tank, i put my fingers down in it to stir it up and the smell was disgusting


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## Scuff

Alasse said:


> They are anaerobic bacteria spots...or heading that way...if you disturb them they stink
> 
> I had some appear in my 1st sand substrate tank, i put my fingers down in it to stir it up and the smell was disgusting


Not that close to the surface. The first inch or two of sand is an aerobic area. That's just simple algae developing.


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## beaslbob

You can test it to see if it is algae by putting some tape over the area to block light. IF it dies off then algae or cyano.

Or basically do nothing. As the plants expand the nutrients causing that black spot should be consumed by the plants.


IMHO there must be a godzillion things in newly setup tank that go away as the tank matures. The key is to prevent things like ammonia and co2 which the plants consume while returng oxygen.


my .02


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## Niki7

ok thanks very much I appreciate it. I just didn't know if I should stir it up or just leave it. Didn't want to disturb it if the result would harm my fish!


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## Alasse

Scuff said:


> Not that close to the surface. The first inch or two of sand is an aerobic area. That's just simple algae developing.


Actually yes that close to the surface. Mine was very similar in placement and it definately was not algae

You can see the same thing developing in my old tank on the right hand side of this pic


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## NeonShark666

The problem with sand is that it tends to compact and decompose organic matter without O2. If you probe the black area you should get bubbles, either Methane or Hydrogen Sulfide. Unlike Saltwater, there aren't many creatures in Freshwater that will burrow into the substrat and open it up.


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## susankat

beaslbob said:


> . The key is to prevent things like ammonia and co2 which the plants consume while returng oxygen.
> 
> 
> my .02


If you need to prevent co2, what is the point of co2 injection in high light tanks? Co2 is needed by plants to really thrive and it also helps to prevent a lot of algea.


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## beaslbob

susankat said:


> If you need to prevent co2, what is the point of co2 injection in high light tanks? Co2 is needed by plants to really thrive and it also helps to prevent a lot of algea.


I give up. What is the need? 

From what I hear with the higher lights the plants become co2 starved so the added co2 just helps the plants thrive and lower nutrients. So the co2 is still much lower then if the plants were not there and co2 was not added. But I understand you can inject too much co2 affecting the fish and causing algae.

Of course the high lights themselves probably also contributes to algae.

I just use lower lights, more fish and not inject co2.

my .02


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## Alasse

You dont want to limit CO2, plants require it to thrive. The higher the lights the more plants will use and the quicker they will grow. CO2 also prevents algae in high light tanks due to making the plants thrive out competing algae for nutrients. Too much CO2 would only be a problem for the fish, as it lowers PH and at night in a planted tank the plants would also be adding CO2 into the water, many fishkeepers find their fish gasping at the surface. Many turn off their CO2 at night for this reason.

Very high lighted planted tanks without CO2 will become an algae field in no time

In my low light tank, i have no surface agitation to keep as much CO2 in the water as possible so it available for my plants to use.


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