If you have a cartridge filter do not put the tabs in the skimmer. Might be ok with a sand filter but trichlor tabs are VERY acidic and can damage pumps and filters if put into the skimmer. They most probably will damage a filter cartridge but sand and DE filters won't be as suseptable. Get a floater for the tabs (they are cheap enough). check around, you want the kind that allows you to adusts how big the slots are so you can control the clorine. some floaters have holes you punch out and if you punch out too many you cannot lower the amount of chlorine you feed. Do NOT just drop the tabs in the pool. they will beach out your liner and the low pH will damage it where the tab sits.
You are making real progress here. You still need to check out Walmart and see if they have the aquachem 6 way test kit that uses reagents. If they do get it! You are going to need to test for more than just TC and pH. You can test at the pool store but the fact that they combined the copper and iron readings in one test disturbs me. I don't have a good feeling about that store.