Tetra's innovative gel feeder blocks contains no plaster and feeds for five days. Blended with patented ProCare for optimal health. Tetra features provide real nutrition to fish when they need it. Allows fish to eat when hungry vs. plaster feeders the dissolve. packed with Tetra's patented, health enhancing ProCare ingredients. It will not pollute water or negatively effect water quality. Gel blocks may be left in the aquarium when regular feeding is required.