Could you explain what affects glutamate and gaba balance and how they compete or balance? I.e. what could cause glutamate to be high, and would than in turn cause gaba to be low?

Glutamate is converted in to GABA by neurons containing the enzyme glutamic acid decarboxylaze.  The GABA in turns acts as an antagonist to the remaining glutamate.

Glutamate is excitatory as where GABA is inhibitory so they work in balance.

Drugs can affect levels or activity of glutamate and GABA.  Caffeine for example increases glutamate activity and decreases GABA activity.  Alcohol on the other hand increases GABA activity while lowering glutamate activity.   Sedative hypnotics can increase GABA activity, but with long term use the brain will adapt and compensate by increasing glutamate production and release.   During withdrawal of sedative hypnotics there is a drop in GABA and the excess of glutamate predominates.

Some drugs, including the antibiotics penicillin and ciprofloxicin, antagonize GABA.

GABA release can be inhibited by neuronal damage such as from high ammonia, hypoxia, ischemia, etc.

Deficiencies in certain amino acids such as glutamine or taurine can reduce GABA levels.  Low carb diets can increase GABA.

Low GABA can be from nutritional deficiencies such as B₆, genetics, chronic stress or high insulin.

Glutamate can be increased by high glutamate foods.

Also - what role does calcium play with glutamate, I heard the 2 were a bad combination, and some use an anolgy that glutamate is a gun and calciuma bullet, but what damage would it be causing?

This is somewhat misleading.  Glutamate increases intracellular calcium leading to mitochondrial dysfunction and cell death.  With all the calcium regulating processes in the body the calcium that can cause the damage will be present regardless if supplementing with calcium or not.  Taurine supplementation though has been shown to counter this effect. Since taurine is also part of our diet this is going to explain in part why glutamate does not always cause this problem despite the presence of calcium.