Usually a soft cloth and water will do: because they are nonporous, glass tiles are typically very easy to clean. For stubborn dirt, commonly available commercial ceramic tile cleaners may be applicable – check with the manufacturer for recommendations.
The answer probably lies underneath the surface. For clues, look at the type of cracks. For example, if a crack has developed across two or more tiles, then it is likely that the substrate is giving way. If the cracks are isolated to individual tiles, expect the adhesive to have been applied incorrectly (too thick and too wet) and now the shrinking adhesive is causing stress on the glass.
Install glass tiles over stable substrates and follow the manufacturer’s instructions. Our experience is that most installation problems can be avoided with the proper use of a crack-suppression membrane and thinset.
There is something chalky looking on the surface of my tiles. I haven't been able to remove it. Any ideas?
If the residue is caused by abrasion, it will be difficult if not impossible to remove. Glass tiles should never be scrubbed with abrasive tools or fabrics.
In some cases, minerals from hard water can leave a residue. Try white vinegar sprayed directly to the tile. Rinse and neutralize with baking soda. Some people have had good results with commerical toothpaste – though abrasive, it can be fine enough not to scratch tile. Test it on a less visible piece of tile first. If this doesn’t work, try googling manufacturers of descaling products like Descale-it and ask if the product is indicated for your tiles.
The pros sometimes use a 10% solution of muriatic acid. Caution: muriatic acid is a very strong acid. Keep the room well ventilated, wear gloves, and keep the acid away from exposed skin; rinse tiles immediately after use.