Small black bugs

Can some body help me out i noticed two weeks ago my girls was looking good and going thru all this weather turning cold i found one of my pots plant wasnt looking like it did it had slowed growth i inspected it and found small black bugs running around on top of soil i noticed on my leaves some coloring yellowing thanking it was liking nitrogen it wasnt that please answer my question on what can i use to kill anything in my soil
 
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