Hi, I’m late to the party here but adding some data from my research.
I agree that you should stay away from ion exchange media. It’s not needed in a planted tank.
As for activated carbon, it depends on the type of activated carbon that you use. There are different types of carbons each made with different materials, technique and pore size. Some are designed to purify air or gas, others are designed for liquids like water. The air or gas ones are more common and cheaper but come with a very small pore size. Obviously, as it is designed for air. Sadly, a lot of what you find in the LFS is cheap and designed for air, not water. This has a tendency to remove more of the chelated nutrients in your water. I wouldn’t recommend.
On the other hand, activated carbon designed for liquids, like bamboo charcoal, has a large pore size and removes very little of the chelated nutrients. This is the type ADA uses and the type I recommend.
Like ADA recommends, it is a good idea to use carbon after aquarium setup as it helps to remove a lot of free floating elements including DOC that has a tendency to be fuel for algae. It is slowly removed over time and replaced with biological filtration material.
After this initial phase, it can be used tactically. I use it to remove treatments for fish diseases or after a significant replanting that has disturbed a large portion of the substrate. I also use it once or two a year to remove tannins from the water that reduce lighting.
Believe it or not, tannins will accumulate in your aquarium even if you don’t use driftwood. Although it is difficult to see in an aquarium setting, they are tinting your water. It has also been proven that they can reduce the light reaching your plants by as much as 30%. Therefore, running carbon to remove it periodically is a good idea.
If you want to get a feel for this, get yourself a white bucket and put water in it during a water change. Compare that to pure water, either tap or RO. Unless your tap is really bad, you will see a visible difference between the two.
Another reason to run it periodically is the amount of DOC in your system. It has been anecdotally stated that this can lead to increases in algae. Therefore, reducing it might be beneficial to your system. Carbon is one way to do this.
Remember, when you do a 50% water change, it reduces DOC too but only by half. This, over time, causes an increasing level of DOC in the system. To reverse this and bring it to zero, periodically, I do a 50% water change followed by a week of carbon. The carbon will drive the remaining DOC down significantly. It’s a type of resetting.
In the end, is this necessary? No. However, I feel it does help my aquarium’s stability and is part of my husbandry to keep algae at bay and getting the most PAR out of my lights.