Usually for the first time charging a credo you would use a 50-50 distilled water solution and Propylene Glycol solution, then only distilled water after that. The reason for that is the 50-50 solution helps retard mold and actually helps with the regulation of the water evaporation as the PG helps the foam retain the water longer. As the PG solution will not evaporate you will only need distilled water there on out to charge it again.
For the first time take your credo, and fill it so the solution will cover the top of the grill, and wait for it to be absorbed. Do not overfill as the solution when placed in the humidor could drip onto your sticks. If there is excess solution take it to the sink and shake the credo to remove any excess, do this until no more solution drips out, wipe dry with a towel and then place it in your humidor.
Hope this helps.