I've used it decently a few times and I is not so dangerous. Though, I have fish-less tanks mainly. It has effect on higher plants for sure, I noticed myself that maybe cause of peroxide usage or sth else it took them some time to recover and start growing again. They don't rot. But I fight with BGA for some time and was really pleased it can be reduced this way quite cheaply and easily, tank is perfectly clean and you got a new chance. But it's necessary to change the cause.