Can I use coco liner in a birdbath & would I also need to use pebbles?
Certified GKH Gardening Expert
The problem with using coco liner for this application will be that it will rot over time. This will lead to a nasty mess. There are many things that will be useful for your application, though.
Apart from pebbles, you can use Grow Stone, clay pellets, or any hydroponic medium.
Now, if you intend to keep the water changed, and keep an air pump to keep it from getting stagnant, then it will be ok to use a coco liner. It will be important to treat this as a hydroponic system with weekly, or at the very least, monthly cleanings though.
Here are some ideas for creating water gardens that you may find useful: https://www.gardeningknowhow.com/ornamental/water-plants/wgen/pond-and-water-gardens.htm