The PH Minus and the PH decreaser are both just dry acid and should be fine to use unless they list some other unwanted ingredient on the label. If it is just sodium bisulfate, that's ok. Do NOT use the chlorinating tabs since they have copper in them. You do NOT want copper in your pool. And you're right. Do NOT use the HTH Algaeguard.

I'm not sure of the best way to dispose of the unwanted stuff. Ben will have a better idea. I'll ask him.