I've had good results with 3 ml of lemon juice per gallon before. Never tried cream of tartar.
You may want to use the best chemical detector we have at our disposals. Our tongue.
Fermenting: Blackberry Wine
Aging: Mulberry Wine, Mint Mead, Dandelion Wine, Mesquite Mead
On Hand: Peach Mango Wine, Huck's Cider, Mulberry Mead, Orange Spice Mead, Cyser, Apfelwein, Maple Cinnamon Mead, Hard Cider, Brown Sugar Cider