Drug Use In Non Custodial Parents' Household

[STM101]

I recently discovered that the apartment my daughter's father shares with his mother has apparent drug use. My child's grandmother regularly smokes marijuana and not for any medicinal reasons. I've seen the pipes and I've smelled the marijuana smoke. I've overheard her on the phone with her sister saying she needs more pot from her. I find it very unsettling that the place my daughter has to spend time with her father has such flagrant drug use. I'm at a loss for what to do. Her father knows of this drug use and says that it's only marijuana and she tries not to do it in front of our child. I've called the local non emergency number and I was told there was nothing they could do unless I had definitive proof, they failed to elaborate and were not much help at all. He does currently have visitation rights through the courts; I don't want to completely cut him off from his daughter I just don't want my child in a home where illegal drug use takes place. Is there a solution to this problem other than him moving into his own place, which he refuses to do because he cannot afford a place of his own. Any help or advice would be greatly appreciated.