"I suggest you talk to a fertilizer company."

I'm the research director for a very large horticultural corporation. We use copper tubing in our multi-stack NFT systems with all sorts of fertilizers. We have no issues because we got non-treated copper piping.

And our systems have been in operation for two years easily and still produce great crops.

And we use AC for electroplating copper into wafers to fill damascene structures, so your statement of using only DC for electroplating is false. There are issues with using AC for electroplating, such as deposition morphology, and the consumption of organic additives. To work around this, we use different copper alloys like CuSn, or CuMg, CuZn, CuPd, and other copper alloys.