This is the safer way all the way around. Sure don't want someone showing up at your house asking about all of the water running down the road

This also keeps your plaster protected.
You might need to do it a couple of times to get your numbers where they need to be.
For you CYA test do this for me:
-pull some pool water
-have some tap water ready
-put the same amount of pool water and tap water in a measuring cup. Maybe 1/4 cup of each. Mix it good
-now use the mixed tap/pool water for the CYA test.
-You will DOUBLE the number to find your CYA amount.
Doing the CYA test:
-GLANCE only!! Do not look for the dot. GLANCE in then look away.
-Pour to each line starting at 100. If you see the dot at a GLANCE then pour to the next line.
Kim