Ceramic Water Filters for hiking and camping

I was looking at the Ceramic Water Filter Candles for portable systems. The question(s) came up:

 How many gallons will the filter provide before it goes bad for the 7" Supersterasyl and 10"?
 Since there is the 7" and the 10" Supersterasyl candle filter, will this change many gallons each one will provide? If more then one candle is added to the buckets will it increase the amount of gallons before going bad? 
Are the candles re-useable and if so how long?
Will the thickness of the filter change the difference of the water provided? Is there a re-useable candle?
I'm asking these question(s) because our family we go out hiking and camping for long period(s) of time and we would love to find something that can fit our lifestyle, we really don't want to end our trip short because of lack of drinking water.

The CN-SS 2"x7" Supersterasyl filter candle has a 535 gallon capacity, whilst the 2"x10" ceramic candle has a 750 gallon capacity rating. It make it easier to use the same size candles for determining the replacement frequency. Essentially, however, you can get about 1,285 gallons of filtered water before you need filter replacement. The more filters you use within the system, your move overall capacity, as well as, production (drip-rate) you will receive achieve.
All of our ceramics, including the ones mentioned above and below, use what's called a Sterasyl shell (membrane). We sell a Sterasyl filter which does not contain activated carbon inside to reduce chemicals, taste and odor. The Sterasyl is simply used to remove suspended solids and micro-organisms from the untreated water. It is because it does not contain any GAC inside, that these filters can be cleaned over 60 times and not need to be replaced for several years. This model is CN-S, and is located on the following link http://doultonusa.com/HTML%20pages/ceramic_candles_gravity.htm with Doulton other gravity filter candles.