a. Carbon Block is a solidified form of honeycombed carbon. It is the best form of filter but flow rate is significantly slower than with loose charcoal.
b. Activated Silver Impregnated Charcoal. Sometimes called Chlorgon, this adds chloramine exclusion and bacteria killing ability to the basic carbon.
c. Micron Rating.
Anything 1 micron rating or below will inhibit Cryptosporidium and Guardia as the cysts are larger than this in size. Viruses cannot be inhibited by a filter with a micron rating of more than 0.01 microns.
Carbon filters cannot change the pH balance of the water. If you have acidic water, you will still have acidic water, as the minerals causing the acidity will be dissolved and therefore will pass through the carbon filter.
Carbon filters may be susceptible to mould attack if left unused over extended periods. It is important to realize that a filter gathers the ‘garbage’ in your tap water, and the organic component of this garbage is quite capable of rotting. Add a little summer humidity to the already damp internals of a carbon filter and you may have a mould attack. Taste will always be the deciding factor, and if the taste of the water suddenly changes after an extended period of non-use, such as your annual vacation, change the filter.
Note also that carbon filters reduce in efficiency the longer they are in use. For this reason regular filter replacement is essential.