I just went to Puritan.com to check out the Magnesium Malate that they sell. I wanted to compare that label with the label of the Malic Acid they used to sell. We do want to compare apples to apples. 
I take 3 tablets a day of the Malic Acid they have stopped producing. I had a stash in my closet. I took that much because the studies showed that you needed at least 2,400 mg. of malic acid for it to help with pain. Each tablet has 825 mg. of malic acid so I am getting 2,475 mg. of malic acid.
These same tablets contain 152 mg of magnesium so I am getting 456 mg. of magnesium in the form of magnesium malate by taking three a day.
Puritan has discontinued this product and has replaced it with Magnesium Malate. A serving size is six capsules. If you take six a day, you will be getting 2,500 mg. of malic acid and 433 mg. of magnesium malate. So, as you can see, they are almost identical except for the fact you have three more pills to swallow. I would spread the six out during the day. I usually take mine twice a day so I will take 3 in the morning and 3 in the evening when I end up buying more malic acid/magnesium supplements.
Why malic acid? Basically, malic acid is necessary for the conversion of glucose to energy in the mitochondria of the cells. In the mitochondria (energy factories) of our cells there is a phenomenon going on known as the Kreb's Cycle. It converts glucose into ATP which is the energy that powers our body. In order for this to happen we need to have sufficient levels of magnesium and malic acid present in the cells. It has been noted that fibros and choronic pain patients have low levels of malic acid present in the mitochondria. To counter this, additional amounts of malic acid can be consumed to make it available to the cells. When malic acid and magnesium is very low in the mitochondria it can lead to fatigue, pain from built up lactic acid levels and the loss of muscle strength. ***This paragraph was written by a former mod named Jeannie. She used to be a nurse. She got me started on malic acid and it has helped me a lot. It doesn't help eveyone but for those it does it is a God-send.*****
Sherrine