In a large bowl, combine sliced cucumbers and salt. Mix well and then let sit for 1 hour.
In a medium saucepan, combine white and brown sugar, white vinegar, apple cider vinegar, mustard seeds, celery seeds, turmeric, and dried onion flakes. Simmer over medium-low heat until sugar is completely dissolved, stirring often.
Rinse salted cucumber slices and drain well.
Place the drained cucumbers in with the hot vinegar mixture. Stir and cover. Let stand at room temperature for 1 hour.
Transfer cucumber mixture and brine to jars, pouring brine into jars until covered to the top. Cover with a lid and refrigerate. Pickles are ready to eat in 24 hours and will hold refrigerated for up to 3 weeks.