Generally, for canister filters, the water flows into the canister and down the outside of the media baskets.
Then the water is drawn up through the media baskets and returned to the aquarium.
You should have coarse filter media first, like a sponge, that can be easily rinsed, because it will trap the largest debris,
and by first, I mean in the lowest basket in the bottom of the filter.
Then in the next basket, you should have filter media that will host the nitrifying bacteria culture, this could be filter floss,
ceramic media, bio balls, plastic scrubbies, or anything that has a large surface area to host bacteria.
In the last (top) basket, will be the finest filter media like a fine sponge or a sheet of finishing filter media to trap fine particles
before the water is returned to the aquarium.
Here is an internal diagram of your canisters:
Since you have two canisters, try cleaning them a month or two apart to make sure there is a thriving bacterial colony in your system.
If your tap water has chloramine or chlorine in it, make sure you treat the water in a bucket first before using that water to rinse the
filter media or fill up the canister before returning it to service.
Good Luck with your South American cichlids and large aquarium