Coco fiber does not cause impaction. The only way this substrate causes impaction is if there happens to be a large ball of the fibers clumped into the soil and they eat that fibrous lump which I have even seen passed by the frogs. Coco fiber is safe, but in any case you do not want them eating substrate. Tong feeding is best.

Also a 20 gallon is much too large. New frogs should be kept in small enclosures. Especially babies. Babies should be kept in medium to large critter keepers to allow them to not be overwhelmed by the large space. They tend to become very stressed in large enclosures. Even juveniles should be kept in these size enclosures until they are large enough to be placed in a larger tank. Even so a 10 gallon is the most suitable size Sven for an adult female because even as adults they become overwhelmed and stressed by large open spaces. Also the reason for babies and juveniles to be kept in smaller enclosures is due to their need for a lot of food an nutrition needed during these crucial growth stages in their lives. They need to have food easily available and easy to catch hence the smaller enclosure.

You will learn a lot from your frogs behavior. Pay close attention to its habits and reactions to your presence. It takes Time for them to get used to you and trust you. Once you are no longer seen as a threat the frog will feel more comfortable and not hide from you nearly as much. Especially when it learns that when you're around it could mean food. Pacman frogs are nocturnal so they should be Fed at night. Be sure to cover 3 sides of the enclosure with some sort of dark background so the frog feels more secure and provide hiding places as well like fake plants with large broad leaves for cover.