Any magnesium causes hydration of the colon, making the stools more fluid. The magnesium citrate is water soluble and more easily assimilated into the body. The softened stool is evidence that your body did assimlate the magnesium. I think magnesium glycinate is fine if you normally have a soft stool. However, the citrate may be best for we who suffer with constipation.
Very loose stool is the common symptom of taking more magnesium than the body actually needs in conjunction with your calcium intake. Simply take less magnesium. There is no set rule on how much magnesium you need since our needs are specifically our own. There is nothing that can tell you exactly how many mg. a day you as an individual need. You find out on trial basis. If you intake more calcium for instance you may find you need to balance it with more magnesium, and vice versa. I only need 400 mg. of magnesium citrate a day to avoid deficiency symptoms.
Diarrhea is the common sign of too much Magnesium per calcium intake. Instead of changing magnesium type, you can back off the magnesium to find your own mg. need, and avoid over supplementation.
The book, The Miracle of Magnesium, by Carolyn Dean M.D., also a researcher and naturopathic doctor, states that a lack of magnesium causes cramping, jerks, tics, muscle spasms and hiccups.
However from my own research I find that a deficiency of balanced B vitamins affects the nerves so that deficiency also causes tics and spasms and too loose stool (Pellagra). We need B vitamins for feeding the nerves.
Almost every person is deficient in B Complex vitamins, since B vitamins need to be naturally balanced and are mostly obtained from raw whole grain, and most grains are refined and cooked before we eat them (such as wheat). And B vitamins B's are water soluble so whatever your body does not use that day is washed out of the body. B is not stored in the body like vitamin A, for instance. The body is easily B depleted every day.
I suggest that at first, to replenish your body, that you take B vitamins in the pure and balanced form, such as in bulk brewer's yeast (not capsules) and/or in carob, at first. In America, these foods can be gotten at a health food store, or you can order online. Any brand is fine as B is very digestible and easily assimilated.
Start with one teaspoon of brewer's yeast mixed into some orange juice or water (some like apple juice with it), or sprinkle one teaspoon of carob powder on sliced or mashed bananas. Have this once a day, then in a week work up to two teaspoons a day. It is not toxic.
Your body uses what it needs and the rest is washed out in the urine. The urine might turn yellow. That is just the normal coloring from the B vitamins. The only reason for increasing the dose slowly is that brewer's yeast can cause gaseousness in the bowels. That is from growth of the beneficial bacteria in the intestines. Increasing the dose slowly lets the body adjust without too much embarrassing gas.
You may notice improvement in as little as a week. After a couple of months, you can switch to B-50 complex vitamins in capsules or pills. One of these should be taken every day. Our nerves (and skin) really need B complex. Well fed nerves handle pain better, too. B complex definitely raises the pain threshold.
Or you can take just Vitamin B 50 (or 100) B Complex, any brand is fine.
I use magnesium citrate and B 100 Complex vitamins with great success.