I absolutely agree with RollTide as I've also been there done that. (All though I stuck to the cheapies on ebay/amazon). I always blew a 0. He'd blow a 0.11-0.5% but would swear with such conviction that he hadn't drunk I just didn't know what to believe. He'd also come up with the stupidest excuses that I would think just might be true. He's used mouthwash, he's vomited, his medication was messing up the tester.
I used to be at home in the evenings testing it out with different ways. I'd use mouthwash and blow a .2%, then I'd take a drink of water and blow a 0, so then I knew it could only be the mouthwash if he did the test almost immediately after brushing his teeth. If I ever went out and had a drink I'd take the test to be sure it worked. Then as soon as I knew 100% that the test was accurate it 'mysteriously' disappeared. So I'd order a new one and have to go through all the checks again before I would trust it over him.
Eventually I we had a session together with his psychologist, (an alcohol specialist who I also used to attend a family group with). She basically told me not to be driving myself mad and that I should trust my own instincts. Basically that I knew full well whenever he was drunk and didn't need to justify my suspicions to him as it only gave him new ways to make excuses while upsetting myself.
I've got to say OP, I'm sure you love him, but if you can easily extricate yourself from the relationship you should be at least considering it. If I could meet myself of 8 years ago I'd tell myself to run and run fast. I really love my husband, when he's consistently sober he's a wonderful, funny, intelligent person, who I just bloody click perfectly with. I'd never want to be with anybody other than him, he's my soulmate. But the lying, manipulative gibbering moron he becomes when he's drinking is just not worth being around and is cancelling out my love for him. He's been going through an extremely tentative recovery recently but I think he's sliding back toward his old ways. I've told him tonight that if he does we are over, and if we are my biggest regret will be the time I gave him.