Agree with Ryan in cleaning up (catch with a small brine shrimp type aquarium net) any poop as found. Amount of water changed will depend on filter, water volume, and frog activity. First you need to let filter cycle and get colonized with bacteria. It will take around a month to do so; but you can accelerate process by using a product like Seachem Stability, usually done in two weeks.

Once cycled and there are no Ammonia or Nitrites in water; then you measure your Nitrates and do a 10% water change. Measure the Nitrates again a week after and you want them around 25 ppm. or lower. If higher; then increase the weekly water change volume accordingly. Once dialed in; then just stay on schedule and clean filter (with tank water during water change) when flow starts to slow down from normal. Good luck !