They key to good regulation is this. 1. Do not over saturate your Credo. 2. Exposed surface area.
The larger the exposed area, the quicker the credo can react to flucuations in RH. Therefore, if 2 credo's given the same amount of 50/50; one 3 in x 5 in x 2 in deep, and the other 2 in x 5 in x 3 in deep, the fisrt one will regulate changes in humidity quicker. Both have the same volume.
On a second point, distilled water will evaporate at a higher rate than PG. Over time, if you only add distilled water when the RH drops, you will lose the ability to absorb humidity from the air. So intially, when you charge the credo, it is 50/50. The next time you add H2O, you aren't matching it to how much PG is left. If you add until it seems like the same amount as the initial charge, you are adding too much water. Because some of the PG evaporated also. Key is you will have to play with it a little by little to level out at the RH you want.
When I recharge my credo in the humi, I add 2 parts 50/50 to 1 part H2O. This works for me, because I am in a humid area and don't need to much H2O. For someone else it could be 2 parts H2O and 1 part 50/50. Someone like Joe M. out in the desert might not add 50/50 for 2 years, only H2O.
So, if you want a truely stable system, go with Climmax. If you don't mind tinkering around, PG and credos are just fine.
Emo