New Bristlenose Plecos - Dead and bloated fish

[Perglint]

Hi all, first time posting here, so please excuse me if I do not have the right forum etiquette!

For context, my tank details are the following:
64L (17 Gallons), using a canister filter.
4 x ornate tetras
5 x glowlight tetras
4 x cardinal tetras (exc. the one that just died)
2 x bristlenose plecos (recently added)

Everything started a little over a day ago when I went to a new fish store as my previous has shut down. I purchased two bristlenose plecos (each roughly 4.5cm / 1.8 inch), upon adding them to my tank, I noticed one of them had a bent pectoral fin. Then fast forward to today where I woke up to one of my cardinal tetras dead, caught behind the filter intake. This is when I started to assume that something from the fish store has infected/polluted my tank. I did a water test, with the following results:

PH: 7.5, NH4: 0, N02: 0, NO3: 1 (previous NO3 result prior to adding plecos was slightly lower, I'd say between 0 and 1)

After the test, I did a 30% water change and afterwards fed my tetras as usual but also added two small sinking wafers (Hikari brand) for the new bristlenoses. The tetras ended up eating their food and then instantly going for the wafers.

About an hour or so after feeding, I noticed that all of the cardinal tetras and half the glowlights were extremely bloated, I do believe the bloating has gone down a little bit but is still very noticible.

At this point, I am concerned with the death of the cardinal tetra which I can't explain. I am also concerned about the bent pectoral fin on the bristlenose and worry in case it is something more severe like fin rot? Should I go back to the fish store and ask for a different bristlenose? I would greatly appreciate any and all suggestions, thank you!!

PS: I also noticed a tetra poke/bite the bristlenose close to their bent pectoral, only seen this happen once so far.

Pictures are attached showing the bristlenoses bent pectoral fin. The dead cardinal tetra (both sides) and the bloated tetras after feeding.

[Colin_T]

Hi and welcome to the forum

The bent pectoral (side) fin on the bristlenose looks like a genetic deformity. There's no treatment for that.

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The dead cardinal tetra is really skinny and has a white patch behind its head. The skinny part could be from lack of food, intestinal worms or gill flukes, worms being the most common cause if the fish is being fed well.

The white patch behind the head could be a bacterial infection. Monitor the remaining fish for any pale cream or white patches and if any show a white patch, post pictures immediately. If no more fish develop a cream or white patch then that is fine.

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The fat stomach on the fish is because they ate a lot and the fish are skinny so it becomes quite noticeable.

How long has the tank been set up for?
How long have you had the fish for?

How often do you feed them and what do you feed them?
Were they skinny when you got them?
What does their poop look like?

The last 2 pictures don't look like cardinal tetras. The fish in the bottom picture looks like a rasbora.