HELP! Tiger Barbs all hit at once

Good Afternoon,

I have a 220 gallon fresh water community tank and did a big water change yesterday (about 30%). All levels were on the money but this afternoon 3-4 tiger barbs are stuggling to swim down to the bottom and have bloated stomachs. I'm assuming some sort of swim bladder issue. I also just introduced some brine shrimp and sinking pellets to the tanks diet of usual flakes. No one else in the tank seems to be having any issues. Any one have suggestions on what may have caused and any potential treatment?

thanks in advance!!

The levels I'm currently reading are 0/0/20. It's weird that only a few fish of the same species were hit, but not all of the species. The water was dechlorinated with an appropriate dose of Prime (not an old bottle). The only thing changed is diet, which is leading me to believe it may be constipation. I introduced freeze-dried brine shrimp to the their diets two days ago and am not just reading about pre-soaking it before giving it to the fish. The Tiger Barbs are pretty agressive eaters in my tank, and there is a good chance that they ate a large portion of that food - potentially leading to the swim bladder issue (my thoughts).