Filter moving substrate

I just set up a 2.5 gallon tank with a Deep Blue Professional HOB. The hob is pushing my ADA Aquasoil around under the output, creating a crater looking dent in the substrate. I've turned down the filter pretty substantial already. Do you have any tips to stop this until the plants get grown in better?

I was thinking about buying some small river stones and putting them where the hob flow is hitting the substrate until the plants grow in more or just letting them grow over the rocks.

What have you done to fix this problem?