The thing to remember is that pH is often a surrogate for mineral content but not always. Its not uncommon for people to know whether their local water is considered to be hard(high mineral content) or soft(low) and sometimes you can get further verification of that by finding the website of the local water authority and checking the data there or calling them and talking to their lab. This saves you the money of buying a GH/KH kit (which is just another two bottle, two testtube kit similar to your master kit.) Of course if you have a GH/KH kit you can get the best data of all, straight out of your tank, but its not usually highly necessary.
Assuming you have a pretty common situation, higher pH numbers like 8+ are usually indicative of harder water and low pH numbers like 6.4 and down are usually indicative of softer water. Remember though, there's nothing that says it -has- to be that way, just that its quite common.
OK, so moving on, its also important for us when we talk about it in our beginners section here to always note that the vast majority of fish we all buy in the typical LFS these days are quite capable of doing ok in most of the ranges of water we might have as long as it is kept pretty stable with respect to hardness (and, subsequently, pH for the most part.) The place beginners get in trouble usually is from dumping in chemicals to alter pH and then doing water changes that alter it yet again, etc. etc. Most of us are better off staying very close to our tap parameters, so that water changes are a natural thing for the tank.
Having said that, we can move on to the more subtle, but real, world of knowing that some fish "prefer" (or might "thrive better" or perhaps breed) water at one end or the other of the pH/hardness spectrum. There are tons of species out there but just to pull some common examples.. livebearers (that you asked about) (mollies, platies, guppies, swords, endlers etc.) are usually at the "hard" end of the spectrum. Species originally from the Amazon basin are usually at the "soft" end (neons, cards, angels and more.) Cichlids can also be pretty dramatic about this and different species come from different lakes with different water characteristics. Seeking out these details and have a "species specific tank" is, by the way, a branch of the hobby.
...don't know why I got off on all that when the I suppose my answer to your question was just Yes, livebearers should like your 8.2 pH! lol
~~waterdrop~~
