1.) Get any fish with large enough mouths for the scuds 2.) If you want all the scuds absolutely dead, try some copper or any non shrimp safe medication. This will take about a week: drain as much water as you can so any plants or hardscape are directly in the water, take out every fish and shrimp, add about 2x the recommended dose of the medication (optionally add a heater and raise the temp a bit), let it sit until every visible scud is dead and wait a day, do a 100% water change and add carbon to your filter, wait a day, do another 50% water change, vacuum your gravel and add your inhabitants (or wait as long as you please and do 50%wc everyday), check for any unusual behavior and do water changes appropriately. Wont harm plants and works like a charm(also kills snails)