New to Discus - Need assistance all the way

[syedilyas8]

I recently bought 4 discus (Had 2 long back and died as I dint do much research on them), juveniles and well settled. Blue diamond, two red torquise and another is some kind of red map or checker I think.
Two of them are slightly bigger than the other 2, they keep chasing them but all are eating well and look healthy. the smallers ones are very careful eaters, initially I thought they have some issue. but by observing found out they are eating smaller food due to their mouth size and the bigger ones eat anything I give.
Initially when I bought them they dint eat tetra bits. I was scared (althought I knew they will go weeks without eating before they settle), so was panicking what to feed them. Beef heart was not an option here. I got them dried worms, flakes etc. but later to my relief they started eating everything. I haven't measured PH yet (know its very important and I am trying to buy one ASAP). do water changes every 3-4 days. my tank is a 20 gallon tank (trying to get a 50 gallon soon, may be this week itself). Kept temp at 30c.
all have high fins and I have added nitrifying bacteria recently and Epson salt to keep the parasites and nitrates at bay. I have a bare bottom tank and run a sponge filter and top filter (this is a really good filter as it doesn't let any dirt sit at bottom and the waste is never dissolved as the media sits outside water).
This looks like a happy discus set up but again as I read about them I find this not a fish for everyone. But yes I would like to keep them. I wanted to make perfect set up but will take some more time until they show growth and that they are happy with me.

my problem: although all seems perfectly fine, two bigger fishes breathing is slightly more than the smaller ones. although its not rapid breathing but I am worried. Their diet hasn't changed and they seem ever hungry.

recently I did a PP dip, do constant water changes, added Epsom salt and nitrifying bacteria too. I want to know is this breathing normal or is this a symptom to something hidden. plz advise. I will try to post video of this soon.

[FishFanMan]

How large are your 4 discus you presently have in your 20. Is your filter cycled? If your not sure do a 75+ % water change at least once a day. Do you have a test kit for ammonia? Use that everyday to make sure you don't see any ammonia in the tank. If you do a big WC every day and they're eating fine. Sounds like you are doing well. But it depends on how big they are. How fast are they breathing, like per minute? 60 or 120 per minute"