5 Colo. Code Regs. § 1003-5-3.13
All diatomaceous earth (DE) filters, whether of the vacuum or pressure type, shall comply in all respects with the standards of the NSF covering such filters. Rate of Filtration: The filter area shall be such that the rate of filtration shall not be greater than 1.5 gpm/sq. ft. or that specified by the NSF for the specific filter in use to achieve the proper turnover rate for the pool. Where DE body feed is provided, the device shall be accurate, within 10 percent, and shall be dependable. The filter and all component parts shall be of such materials, design and construction to withstand normal continuous use without significant deformation, deterioration, corrosion or wear which could adversely effect filter operation. The filter shall be so designed and constructed to eliminate the possibility of introduction of the DE into the pool. The filter plant shall be provided with such pressure, vacuum or compound gauges as are required to indicate the condition of the filter. All filters shall be equipped for cleaning. Provisions shall be made to completely and rapidly drain the filter. A rate of flow indicator shall be provided on the filter system. Backwash lines shall not be restricted in any way between the filter and the sanitary sewer.
5 CCR 1003-5-3.13