Well, buckets may work with a pump to pump water from the buckets into the tank. I was 60G barrels to age my water. The volume required for the aged water is dependant on your tank volume. The number of buckets you need depends on how big your buckets are. For example, 25% of 75G is around 20G. If you are using 5G buckets then you will need 4 buckets.
What I would do is good to Walmart or Home Depot and look for their Rubbermaid or similar containers. You will be able to find some big containers like 30-50G+ for a reasonable price. Go to Big Als and pick up a pump (Rio's are reasonable, Mags are best). Find some hose/pipe (Home Depot) and there you go! Look thru the diy section for some ideas!
Aged water is basicly water that has been heated and aerated for 24 hours or until the C02 has dissapated!
Btw, are you not buying young discus? Twice a week water changes may not be enough for good growth. Just curious!