I cook my beets in the crock pot until tender, peel and either slice or cut into desired pieces. I then use 1 c apple cider vinegar and then 1-1/2 c of 100% juice (my last batch was white grape, but apple juice or any other works as well-original recipe calls for OJ) and pickling spice and 1/4 tsp salt.
put beets in a jar, pour in the juice mixture, add @ 1 tsp of pickling spice (to taste-more or less depending how spicy you like them) per jar. Add onions if you like. add lids, store in fridge for 24 hours and then they are ready. SO GOOD. I could eat the whole jar if the bathroom episodes did not flip me out. LOL!
My recipe is an offshoot of this one Cooking Weekends: Easy Pickled Beets with Orange & Ginger