While its pretty well not an issue if its on LR opr substrate either with tube in substrate or on top, you will find they do better on substrate with some of the tube at leat covered, as it keeps the tube a bit more protected, but they usually do fine most anywhere. They are not light dependant, like some flow. Just enought flow so they sort of flutter and move slightly, not that much flow that it bends their crowns back or makes them move violently. They can and will move to some extent but not a lot.