Get the OTO / phenol red drops kit, preferably the HTH 6-way (made by Taylor), but if not available, get a cheapo 2 bottle model. OTO is not very accurate but it's VERY reliable, can covers the entire range from 0 - 60 ppm.

Stop using BioGuard products -- they are among the worst about adding mystery ingredients that will screw up your pool. A BIG part of our approach here is to use ONLY known chemicals, and ONLY when there's a clear and specific purpose for doing so. We recommend the "add some and see if it helps" approach very, very rarely.

That's why we steer people to no-name commodity products that are simple, undiluted and unblended.