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From the anecdotal reports I've read, ammonia you're likely to find at wal mart is going to have suficants or other additives you don't want in your tank.
However, ACE Hardware store brand ammonia lists nothing but ammonia as the ingredients and has been the brand of ammonia that has been getting recommend. If you don't have an ACE Hardware near you, I've heard (but not verified) that Piggily Wiggily store brand ammonia is also free of extra ingrediants.
I've also looked at Walmart and didn't find any surfactant-free stuff, even when it was labeled "clear ammonia." I have the Piggly Wiggly brand in front of me though, and it lists only "soft water, ammonia" as ingredients.
I was reading around, and I just so happened to have the old and the new versions of the Wal Mart brand ammonia around. It would seem that they changed their "pure ammonia" to have surfactants instead of chelating agents, because I've cycled a few tanks with the old ammonia and it worked fine.