I think you are fine. If you use bleach, it will try to push your alkalinity up over time, so I wouldnt artificially increase the alkalinity with baking soda. Let it stay where its at.

As for the DPD powder, it does turn gray over time. Its fine. As long as it doesnt have any chunks in it, you should be all right.

You can buy DPD powder from taylor chemicals on line. It only costs a few bucks. www.taylortechnologies.com