There are a whole bunch of factors to how frquent you need to change water, how much to change, etc. Most discus folks do massive, even 100% water changes daily. Typically the need for the 100% water change is due to the fact that you have many juvenile fish (less than 2") in a small tank and you are feeding them 10 times a day.
Unless you are breeding discus and raising them from tiny fry, I would not recommend feeding them 10 times a day. Three to four feedings daily is more than enough IMO. It's not likely that you will buy discus any smaller than 2" and typically most are for sale at the 3" mark or bigger.
Filtration and type of tank setup are other items to consider. Popular amongst discus keepers is the sponge filter. It works well for an in tank source of biological filtration but doesn't "remove" anything from the tank. I like to use a combination of filtration. The biggest filter being a canister. I have an FX5 on a 150 that works very well. I also use wet dry filtration as a means of routing water from the tank surface to the sump. Since my tank is heavily planted, I use the sump to add fertilizers to the tank and the pump in the sump returns the water back to the tank through a CO2 reactor and UV sterilizer.
The reason that I only do water changes once a week is due to the fact that I have a light stocking ( 16 discus in a 150 gallon tank) and the plants aid in keeping the water perameters in this tank pristine! It's a complete biotope. Filters only perform part of a nitrogen cycle breaking ammonia down to nitrite then nitrate. I like using a heavy plant load to help consume some of the ammonia plus they complete the nitrogen cycle by absorbing nitrates.
To some it all up, I can test my water after 7 days of zero maintenance and have perfect readings. The biggest reason to change water at that point is to remove any solids in the tank (poop) and to reset my fertilizer loads. Some ingredients of the fertilizers tend to accumulate. Now, that's what I do.
To give you another perspective, there are some discus keepers that keep 5 or 6 discus in a 100 gallon tank and insist on 100% water changes every day. This also works for them. They also likely have bare bottom tanks and a sponge filter. Changing that much water every day eliminates the need to try and establish a biotope in the tank. It's basically sterile.
Most people will tell you that the best way to keep them is through the massive water changes and huge feedings in bare bottom tanks. It does work, but IMO the biggest reason they do it is because the person that they learned from does it and so on and so forth. Why would you think differently if a breeder tells you that's what you have to do? Good question. Breeders do this because they have hundreds (if not thousands) of fish in hundreds of gallons of water. Plus they are feeding more to get their fish to grow quickly to get them sold. I would do just that myself if I was a breeder. Again, this is just my opinion and observations.
There is a ton of controversial information about this. Read these forums and learn from what other people do. I told you what I have done with my tank. It's 2 years old. I haven't had any dead discus, no diseased discus and I have spawns in this tank weekly. The discus in this tank were purchased at 2" a year ago and range between 4.5" to 5.5-6" today. If the environment in my tank were so horrible from not changing the water every day, I would think that I would have death, disease and would never see breeding. Again, just my opinion. I am no biologist by any means. I'm an aerospace engineer.
Now, when you do have to do water changes, and you should change 50% or more weekly, then you have to be prepared. I have a 100 gallon storage tank in my garage that I age, heat and treat with Prime before adding it to my tank. If you ask around or read more on this site, you'll see people using all kinds of methods. I've seen trash cans, other aquariums, basically anything that will hold water. Find what works best for you. Now, I'm sure you're wondering, "OK, how do I get the storage water in to my tank". Well, you could use buckets, but I don't have time for that and I'm sure you don't either. I use a pump and a hose. The pump transfers the water from my holding tank all heated, treated and ready to go straight in to my tank by way of the hose. I like to drop the temperature of the new water by abou 4 degrees. This is typically when spawning takes off!
I have to keep throwing the "this is my opinion" disclaimer out there because my way goes against popular belief. Read all that you can and do what works for you and your discus. Just know this, there is more than one way to keep a beautiful display tank with Discus, plants, substrate, other fish, etc.
