I went through the same and used hydroguard, I was very reluctant to give it up as well but was forced to ad it's not available here.
Been using Clear-Rez in leu of Zone for the past couple runs. It requires twice the dose if not more. Never tried pool shock, heard alot of horror stories. System is a ebb/flow Grodan Hugo setup with Supernatural Aqua nutes, GH PHup and down and importation of mildly mite invested 3king clones that were also treated with clearez. Have not had any pythium issues for many, many years when using Zone. Had a little round of spider mites so i performed a spraying every 3 days 7 times with a alternating regiment of advid and floramite. Hopefully this still works with mites. Years ago in the past i did it with Zone and had was guarded agianst pythium. With clearez 7% of the starts got pythium. Frustrated, so I looked up the status on DM website and noticed that
Dutch Master Zone is now available through their website. Just orderd new 5gal size. See how fast the transaction occurs. Excited to get things back in a flourishing regiment. Will check with local stores for availability too. Clear-Res works ok but Zone really is much better product. I do the 2ml/gal dose of Zone with every res change and additional top offs. Will check that the dose is still the same.