Some products containing enzymes will help break down and control blanket weed. This does not hurt plants. Barely straw is effective if you provide good water flow through it and replace the proper dose every six months. If you have no plants, you can use some algaecides such as Water Block. Otherwise, secure a good net to remove the excess.
Green water is an altogether different matter.
While this type of algae also provides filtration and impedes some forms of disease, it reverses its cycle at night and releases carbon dioxide back into the water, allowing the possibility of suffocating the fish. Do not use salt to kill microscopic algae . This algae dies too quickly under salt treatment, consuming oxygen and returning ammonia and other undesirable substances to the water. For more information, please see our library article on algae control. All rights reserved.