in the space of this thread
worries about the environment... ie plants/substrate
temperature..... 86f/30c is generally accepted as being perfect, 83f/28c as acceptable in planted tanks ( though not ideal for juveniles)
Feeding....( just feed them loads.)
parasites... non specific
flukes
poor filter maintenance.... (this is the one piece of kit you cannot afford to have fail.)
white poo...
From the video
which is all i have to go on
bright colours
open and erect finnage
active in all parts of the tank.
elevated breathing, but not excessive.
Discus with parasite or disease problems do not behave like this, they clamp fins, hide in corners & turn dark/black, 95% of the time & nearly 100% of the time if the infection/infestation is serious.
It is always difficult to analyse problems over a forum, but here is my take given the info so far
They are basically OK, maybe a little stunted, but that is not a health issue per se
Possibly some low level irritants in the tank, hence the change in behaviour, shimmying etc.
Some feeding difficulties
If they were mine I would
Check your water again, and also the water you are using for water changes.... how do you prepare it ?
Given their reaction to recent water changes the water board may have changed something & this is upsetting them a little.... possibly chloramine, so check for ammonia in the incoming water. Have you changed the way you do anything, new equipment?
Check water temp with a thermometer, electronic or glass preferably, stick on & heaterstats are notoriously unreliable/inaccurate.
Also how much does the tank temp change during a water change?
Feeding... make sure they all get some, & try different types & brands, even live bloodworm if they go off their food. This can cause problems, (because it can
very occasionally contain something you might not want in the tank)but if they are not eating then you have a major problem already. Don't worry about "protein content" or any other rubbish... just feed them loads.
remember, just because you think it is good, or the manufacturer or other fishkeeper says their fish love it, if they wont eat it it is no good for your fish. Make sure teh discus get a chance, often others dart in & the discus loose out.
White poo can be : - tapeworm, indicative of columnaris infection, or just not eating/not eating enough. Discus pass the intestinal slime lining if they do not eat and it looks just like a white poo.... Given the situation I would nearly always go with feeding....especially given their other behaviour., but worms are a possibility....well not now, so we eliminate worms YA?
the above 2 obviously go together, as prazi also kills flukes & many other ectoparasites they are sorted too...
If there is any gill damage... flukes or other contaminants it can take several weeks for gills to repair.
Juvenile discus breath more rapidly than adults, they also breath heavier during & shortly after feeding. Elevated tank temps can also cause it.... 30c/86f max for prolonged periods, O2 levels drop rapidly with increased temps. given their appearance this is not a serious issue.
All medications are potentially harmful ( most are toxic at some level, that's how they kill things), and all will affect water quality to some degree, hence why you don't use if not required, or until you are sure about what you are treating.
I still suspect bloating prersonally, and cutting the dried food will mean less of a nitrate build-up anyway during the 5 days where you can't waterchange. Offer frozen medicated food and some veg during the course of wormer. Like the wormer, cutting the dired food and increasing fibre intake for a short while won't do any harm, but after 5 or so days, go back to normal 
