Guppy flared-out gills

My planted 30 gal long tank finished cycling (30 days, tests looked good) and I picked up 9 guppies on Tuesday 07/28/2020. One female died in the bag on the 1.5 h drive back home. I put the remaining 8 in the display after temperature acclimating them, because I didn't wanna stress them further. I got a closer look at them in the display and one or two may have fin rot (white ringed holes eating into the fin from the back, like bite marks). Because of this I threw in Ich-X, Fritz Mardel Maracyn, and Fritz ParaCleanse all dosed for 30 gal yesterday 07/29/2020. This trio is recommended by Aquarium Coop to not harm invertebrates or the cycle and be safe to dose together. I dosed the display because I messed up and didn't quarantine them first.

After looking at one of the females, now that I think back on it I recall she looked a little strange when I got her but it didn't register, and today I noticed her gill covers are sticking way out and don't lay flat against her body. She is active and feeding.
I have very hard water about 20 drops GH last I checked (it is about 15/16 out of the tap) and KH is 5 drops
831 TDS (was 825 on 07/25 around normal on this tank)
Temp is 80.6 F (unheated, I do have a couple of spare heaters if needed)
PH - PH Pen =7.6 (was about 8 yesterday before meds and reading keeps dropping the longer it is tested and has never given me a steady reading)
PH - Tetra Easy Strips say PH is about 8.2 or 8.3 (which sounds closer to my normal water PH, not sure which is accurate)
Chlorine is 0
Ammonia 0
Nitrite 0
Nitrate 20

Will I need to treat her differently with something else than I am currently using? Anyone know what could be wrong?

It could be gill flukes.
Is the fish breathing fast?

The Fritz Paracleanse contains Praziquantel which should be able to treat gill flukes.
But treating gill flukes may take up to a month or more due to the parasites eggs that can lay dormant for a long time.

By the way, what are you using Maracyn and Ich-X for? I am a very puzzled.

Add 2 heaped tablespoons of rock salt for every 20 litres (5 gallons) of tank water. Keep the salt in there for 2-4 weeks and see if it helps.

I didn't get a good look at the fish in the store and many of the ones I bought had issues. This female with the gill issue seems to be moving her gills a little faster, her tail looked in bad shape too. If you see in the photo it looks like her tail was bigger or deformed because there is a small amount that sticks out more than the rest?

There is another female with two large half circles taken out of her tail with a white ring around the edge of the missing pieces, I thought the second female had fin rot or bacterial infection so I dosed for that too (which is why i used all 3 meds that I did).

I think that second female (the one with the fin issues) now has her gills starting to stick out more than yesterday (so 2 guppies with this). Tested for ammonia and nitrites again today and they are 0 still, nitrate is about 10 or 15 ppm.

I dosed all 3 meds because of the gill issue in one of them, the infected/damaged tail in a second, and there was a male that looked like he had tiny bumps on him, but they were not white bumps. He is very colorful (yellow, teal/green) so I could only saw them when he was at a certain angle/looking at me. Today (Day 2 of the meds in the tank) and I don't see those bumps anymore on the male.

I really wanted to support my closest mom and pop fish store, 1.5 hours away, but if the fish are this rough I don't think I can.

This is a brand tank set up running for 30 days with plants, gravel, Malaysian drift wood, and dragonstone never had fish in it before. There is some metal mesh that 2 of my java moss came in on in the tank still as well as a sponge filter.

Writing an update for those interested. The two female fish having issues with their gills have had white patches on their scales now as well for a day or so. I've ordered some aquarium salt to try that if this doesn't work. All the males seem ok and the 2 remaining females look fine as well. I had some white growth on an aquarium bulb before I had fish in the tank and feel there may be a connection with this.

I moved both females to a 10 gal quarantine and added 3 tablespoons of aquarium salt. They were doing fine for a day and then the smallest one (first one with signs) died. She had the thickest cottony growth at first. Her gills looked puffy. The second fish she appeared to lose the white growth, but looked like she had wounds on her back down to the skin. She looked pretty beat up, but was swimming around last night before i went to work. When I got home at 8 hours later at 8am she was dead (1 day after the other death). She had 2 red splotches on the back and bottom of her belly that looked like blood under her scales near the anus.

I have the quarantine tank near the bathroom door and either she took a turn for the worse, or maybe the air pump/tank got some contamination from air freshener?

Thanks for the advice that was given. I'll try and treat sooner next time, and be more careful with things in my apartment.