dark spots in sandbed

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New member
The sandbed along the glass of my tank has turned to a dark green/red/almost black color. I can see it though the glass. I tried to take a credit card and scrape it out..but that was not easy. What is this? Is this what others refer to as dead spots..?What should I do. Thanks in advance.


In Memoriam
Hi Sally,

Panic not.

You are seeing cyanobacter growth in the sand bed. It is normal, expected, and indicates the bed is functioning normally.

Let it be or marvel at the neat colors...

This is another way in which the bed functions in metabolizing excess nutrient. Later other critters will eat the cyanobacters, and mobilize the nutrient so that it may be exported. When the cyanobacters are eaten, the nutrient re-enters the sand bed to feed the biological filter and eventually to leave the system as gas, or as some biological export such as excess algae.

There are NEVER any dead spots in a sand bed.

Cheers, Ron
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