A little more info to clear things up a bit. These bugs aren't the same as the ones out in your garden, on your houseplants, or coming from an unopened bag of mulch or potting soil. And what works to get rid of them in a garden setting (lady bugs, soap solution, etc.) isn't going to work inside the home on an aquarium... especially the soap, as that will kill your fish.
I've been dealing with water aphids myself for a long time now. Mine came in with some cabomba I bought from a plant seller... who happened to be growing his in an outdoor pond, along with water lilies and other marginals.
I read several places online which recommended flicking them or splashing them into the water to drown them. That doesn't work either... believe me, I've tried. Not only do they survive that.. they crawl down into the water themselves. So removing your floating plants isn't going to work either all by itself.
At one point, I got fed up with them.... trashed all my plants, left it all bare for several months. Then after I introduced new plants again, they came back as strong as before. Eventually, they also showed up on a second aquarium I have in another room.
That second tank was where I stock my Endler's livebearers... and all those water aphids are gone now. I haven't seen a single spec of those critters there for the last 6-8 months. The Endlers gobble them all up... whereas my goldfish (the other tank) only nibble at them occasionally.
So... to totally eradicate them completely, I'd suggest removing your discus to a temporary setup. Then introduce some Endlers to the infected tank... and let them breed there for a while. After you're sure the aphids are gone, then switch the fish around again back to their original tanks. The biggest problem with this solution, however, is going to be trying to net out all those Endlers from a large tank. LOL. This is what I'm going to do with mine.. eventually... to clear the aphids out of my 110 gallon tank.