While on my adventures of plant shopping, I happened across someone seemingly knowledgeable when it came to potting mixes. She was listing off general consensuses I had found online about the DIY mixtures. I have all tropical plants, except for a few (I have about 23 plants). The one I'm most concerned about is my Mimosa Pudica which has grown exceptionally well the last winter (indoors), with just a 1:1 typical potting mix + perlite. When I up-sized it's container, I read online it's good to incorporate sand into the mixture. While speaking with this worker, they recommended the sand from within sand bags of a vehicle (for weighing it down in winter [Canada]) as the coarse sand options. I hesitated but she highly suggested it. She listed off all kinds of names of plants, mixtures, etc, seemed to know what she was talking about!
I went ahead and used that in any DIY mixes of potting mix for my plants. I wasn't overly concerned about it but now my Mimosa is progressively getting works from the bottom going up. Slowly turning yellow and leaves falling off. Nothing else has changed other than the mix going from 1:1 standard mix:perlite to now 1:1:1 standard mix:perlite:coarse sand. Is there fungi/bacteria/things to worry about within that sand? Also my Moses in a Cradle / Boat is withering away too. Everything else using those mixes are doing fine. The Mimosa Pudica I've had growing since last summer, the Moses in a Cradle / Boat is new so I'm still grasping how to properly maintain it. Also worth mentioning my other Mimosa Pudica (same soil mix) is doing fine.
TLDR: Is sand within a vehicle weigh down sand bag for winter driving safe for potted indoor plants?