I'm going to let Ben discuss with you the specifics about the metals issues.

Regarding testing and getting readings of 3.2 etc. ---- If you use a 25 ml water sample, the multiplier for each drop is 0.2 rather than 0.5 as it is with the 10ml sample. However, we recommend using the 10ml sample so that your testing reagents will last longer. Besides, you don't really need 0.2 precision. 0.5 is good enough!

Tabs can go in any of those places you mentioned. If you do put it in the skimmer, however, you need to make sure your pump does not stay off for more than 8 hours as trichlor tabs are very acidic.