i did this very thing just last summer. I used the sand from my 10 gallon to start my refuge. I didn't have any problems.... i had my 90 up and running though (without refuge) for a few weeks and I used old water from a larger tank's water change. I"m not recomending you do this, I'm just saying that it wont make a difference as long as you let that tank run for a little while and do a little water change just before transferring your livestock. Plus you gotta remember you'll have alot more water to dilute anything you sturr up anyway.