actually, coco fiber has really, no nutritional value for the plants. the frog's waste as well as waste from other critters that may happen upon the tank breaks down and fertilizes the plants naturally. of course, you can speed that process up a bit by introducing springtails and/or isopods. i use a couple of inches of an organic potting soil used for hydroponics growing. it's packed with all kinds of good stuff like bat guano, earthworm castings, sea kelp and yes, it does have perlite in it. am i worried about my frogs ingesting perlite? absolutely not, because it is buried under 2 inches of coco fiber minimum. if i had burrowing frogs (which i do not) i would never even think of using the same soil. all my plants are buried deep, and if i get anything from the lower substrate on the top, i just remove a few surrounding inches of coco fiber and add new stuff in. my plants love it. i also mist them with waste aquarium water.