Owning a flower shop... I naturally use the large rectangular humdifiers filled with floral foam. I saturate them (the first time) in a 50/50 solution of PG and distilled water. I presently have a a 600 ct. Thompson Oxford, a 200 ct. Colossal, 3 100 ct and 3 25 ct. Finally, I have a 42 qt coolerador which has naked oasis foam in the bottom on a bed of cedar.
I check all of the credos once a month and typically recharge with distilled water every other month. My Oxford is the thirsiest and tends to need recharging monthly. For the price, I find standard credos the most economical and when they are filled first with 50/50 PG and distilled water, the always hold a 70% humidity. It never varies... even when it is extremely humid outside (I live in Louisiana where RH is typically in the 90's).
Email me at rpope123 at bellsouth dot net if you need more information or if you want me to send you a block of floral oasis.
Cheers,
grond