Safe to use on plants and fish. Supports aquatic life with an algae-free environment. Helps fish and reptiles to sustain a longer and higher quality of life. Helps to prevent further algae growth. Use one block per 200 litres of water. Gradually dissolves over 7-14 days depending on water circulation to kill organic build-up. Blue Planet products are distributed by Masterpet, a company with over 50 years of experience. Created on the belief that life is just better with a pet, they strive to develop specific products for the specific needs of pet owners. Their products are always known for their quality and reliability. Want to add a bit of scenery and style to your fish tank? !