I Changed To Sand A Few Months Ago All At One Time. I Took Everything Out Including The Water, And Let Me Tell You I Got The Best Tip Off Here. Depending On The Size Of The Tank I Guess. But A Dust Pan Worked Great For Removing The Cc From The Bottom. After I Cleaned Everything Out And Replaced With Sand I Put The Water Back With A Little Extra Premixed Water, And Got The Filters And All Going To, Because I Had A Little Cloudiness, Not Bad Though. Shortly After That I Added Critters Back, And No Problems, No Losses. It Took A Whole Day But Well Worth The Effort, You Will Be So Glad You Decided To Change.