Hi Boltardy and welcome to GoY. I wouldn't put loose soil in the bottom of the pond - it will get very messy. If you want to have aquatic plants use pond baskets with gravel in them. The marginals you will need to plant in soil around the pond.

I agree, any wildlife such as fish will churn it up. Also from time to time I lift my baskets to tidy and reduce/change the plants.

thanks for the answers , much appreciated

You are welcome