A lot of us use starsan as a sanitizer and know of its re-use capabilities. The re-use is ok if the pH level of the solution is under 3. To make things a lot easier and confidence in re-use do what I did, under eBay search "pH litmus paper" I purchase 3 packs of 80 test strips at $1 per pack, postage free from Hong Kong. That's right $3!! Arrived by airmail within 10 days. Each pack has colour comparison strip. Its great, check your spray bottle, rinsing solutions etc. Trust this helps,
Cheers BB