Planaria also burrow under soil.
Personally, I'd leave the seed shrimp alone. It's not doing any harm, and is a sign of a good ecosystem. Products like AE actually encourages small animals to flourish too.
If you have many planaria, after 3 days you can do a second dose for those that are coming out of the soil/eggs. Then after that second 3 days is up, do a water change as some ammonia may be released from the dead planaria. From my experience, shrimp will be fine. Be sure to take some water from your tank and put it into a measuring cup. Mix the powder and water, and then pour it in. The water will fog, but it will clear.
Some people have had good results from the product "no planaria," however from the posts I have seen it's a mixed bag. Some have had deaths of young shrimp from it, some haven't. So I haven't messed with it myself.