In my opinion cellery seed caps are better than nothing. I buy the seeds in a herbal store (one that sells only herbs).
I take 1 tablesp. of seed to brew in a teapot with 2 cups of boiling water. This makes very strong tea which a dilude with half and half water, add lemon and stevia for a delicious drink (sort of). The tea is a little bitter.
I drink the tea through out the day at least 1 day a week.