Is substrate poisonous?

[martinmin]

My 75 gallon tank releases a strange smell, especially after water change. It's black soil for plants. It's a headache. Although the substrate is new, it's almost 2.5 months. Also recently, I am having some cough and I haven't gone to see a doctor. It's a mixture of two substrates. I am afraid it might be poisonous.

Has anybody experienced the same?

 

[Root]

I have an an outdoor pond that is filled with dirt and capped with leaf matter. Anytime I get my hands in it and stir it up the smell can be brutal. 
 

 Here’s a post from another thread that may shine light on what you’re experiencing.