The objective of this study is to compare the safety, tolerability and efficacy of the FDA approved split-dose adult regimen of BLI800 (i.e., two 6 ounce bottles of oral solution, each bottle containing: sodium sulfate 17.5 grams, potassium sulfate 3.13 grams, magnesium sulfate 1.6 grams) to a reduced 3/4 volume of BLI800 (4.5 ounces per dose), as bowel preparations prior to colonoscopy in pediatric patients ages 12 to 17 years.