Cream of Tartar/Lemon Juice instead of Acid blend?

Since cider will have a high level of malic acid, would it be possible to use some household ingredients to increase the acidity? I thought cream of tartar and lemon juice would probably work, but not sure about the amounts because they are not the pure acid form. Maybe a tsp of each? I'm making a cider and in case it finishes soft, I'd like to perk it up a bit if need be and I don't have any acid blend.

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.

What exactly is in the acid blend they sell at the HBS anyway? I've often just used a splash of lemon juice, or some ascorbic acid (vitamin c) powder that I've bought at the bulk store as my acid source (and anti-oxidant) and had great success.

Of course, I tend to do things the cheaper way for such things, so I have more money to spend on quality honey and fruits and such.

I look at the pink stuff my HBS sells for sterilization and gag at the price, when a gallon of unscented bleach costs a dollar, and a few caps full and tap water will create a bucket full of hot sterilizer.