Quick Answer Mills C4 is a concentrated bloom additive for fruiting and flowering plants. It is used as the flowering-stage stimulant within a Mills feed program and is suitable for coco, hydroponic and soil growing media. Select 500mL, 1L or 5L and follow the current Mills growth chart for the applicable week and water type. Product Description Mills C4 is formulated for the bloom phase, when fruiting and flowering plants have changing nutritional demands. Mills describes C4 as its bloom additive, while the official growth charts place it alongside Basis A, Basis B and Vitalize during selected flowering weeks. Application rates vary between the Mills tap-water, reverse-osmosis and high-concentrate programs. For that reason, use the current chart that matches your nutrient line, water source and flowering week instead of relying on one universal dose. Key Features Bloom additive for fruiting and flowering plants Designed for use within a Mills nutrient program Suitable for coco, hydroponic and soil growing media Added during selected bloom weeks according to the Mills growth chart Liquid concentrate supplied in three Shopify sizes Available Sizes and Variants Shopify variant Typical buying need 500mL Trials, small gardens and lower-volume reservoirs 1L Regular home or controlled-environment feeding programs 5L Higher-volume and repeated use Select the required size before adding Mills C4 to your cart. Specifications Brand Mills Product type Liquid bloom additive Intended stage Selected weeks of flowering and fruiting Growing media Coco, hydroponics and soil Use with A compatible Mills feed program Shopify sizes 500mL, 1L and 5L Package Contents One sealed container of Mills C4 in the selected 500mL, 1L or 5L size Directions for Use Choose the current Mills growth chart for your nutrient line and water type. Fill the reservoir with water. Add Vitalize first when it is part of the chosen program, then mix thoroughly. Add Basis A and mix thoroughly. Add the equal amount of Basis B and mix again. Add Mills C4 at the chart rate for the applicable flowering week, then mix thoroughly. Check and adjust the nutrient-solution pH after all nutrients are mixed. Do not premix nutrient concentrates. Add each product separately to water and mix before adding the next product. Follow the current product label and Mills chart if they differ from older instructions. Care, Storage and Safety Keep the container closed when not in use and store it away from direct heat. Keep out of reach of children. Avoid ingestion and contact with eyes or skin. Use suitable protective equipment and follow the current product label and Safety Data Sheet. Clean measuring equipment after use and prevent concentrate from entering waterways. Buyer FAQs What is Mills C4? It is the Mills liquid bloom additive for fruiting and flowering plants. Is Mills C4 a complete base nutrient? No. Mills positions C4 as a flowering-stage additive used with an appropriate base nutrient program. When should I use Mills C4? Use it during the flowering weeks shown on the current Mills growth chart for your water source and nutrient program. How much Mills C4 should I add? The rate changes by week and chart. Check whether you are following the tap-water, reverse-osmosis or high-concentrate schedule and measure the listed rate. Can I use Mills C4 in coco? Yes. The official Mills growth charts state that the regular program can be used in coco, hydro and soil. Can I use it in hydroponics? Yes. Add each concentrate separately to reservoir water, mixing thoroughly between products. Can I use it in soil? Yes. Soil is included among the media supported by the official Mills charts. Should nutrient concentrates be mixed together before adding water? No. Mills cautions against premixing nutrients. Add concentrates to water one at a time and mix thoroughly. Which sizes are available? This Shopify listing offers 500mL, 1L and 5L variants. Does Mills C4 replace Ultimate PK? No. The Mills growth chart assigns C4 and Ultimate PK to different parts of the bloom program. Follow the chart rather than substituting one for the other.