I'm pretty sure that plants can handle H202 for the most part, a lot of people use it for gardening to prevent root rot. Do you plan on putting your plants in substrate at any point? It's usually about the 1 year mark when suspended mangroves begin to die. You may have noticed very slow leaf growth? That's because the plant is putting all its energy into growing roots instead of leaves, and the leaves are what produce the plant's food, not the roots.