Answer:
Step-by-step explanation:
If they live past a week in that water they should be okay. The medicine should only take about 2 days to a week to be in effect. alot of times they say it could be lethal just in case someones pet dies in the time you have the gravel by coincidence and they put that so you dont have grounds to sue them. I am by no means a expert though. But i hope this helped!
-cloudyhelp <3