As long as your pH strips are designed for testing liquids like the kind where you pour the liquid onto the strip, you should be totally fine to use them! Different brands may use slightly different chemicals to show the pH through color changes, but they generally work the same way and are safe to use when making your shampoo. The only type we don’t recommend is the liquid drop-style testers, like the ones used for aquariums. These require you to add chemicals into the liquid you're testing, which not only gives inaccurate results with something like shampoo, but could also mess with your formula. And we definitely don’t want that!