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.