I've been losing panda cories one by one over the last 5 months and despite my best efforts, I have no clue why. I've tried to do my due diligence, but I can't seem to figure it out and my fish deserve better than to keep on dying.
I'll describe the situation more, but first here is the setup:
10g fully cycled for weeks before any fish were introduced
Top Fin power filter 10
No aerator but the filter creates bubbles from outflow.
Thermometer + heater rater for 10g
(I know 10g is considered small, but currently these cories are less than ~1.3in and I'll look into a larger tank as they grow up)
Around 10-15 live plants.
Rocks were vinegar tested and wood was boiled before going in.
Substrate is very fine sand and 1/3 of the bottom is a black gravel, nothing sharp.
initially 6x Panda Cories
1x Mystery Snail
3x Red Cherry Shrimp
Parameters (on average)
Nitrates: always ~25 or less
This is my first community tank. I bought 6x panda cories when they were less than 1in and introduced them into the tank. I lost 1 within days and i chalked it up to bad luck, as it happens. Buried the fella in the garden. 5 left. For reference, I vacuum my tank weekly with a 25% wc
Within a few weeks, another fish ends up dead. 4 left. I observe and count my fish every night. None of them seemed to have any issues or visible symptoms the night prior. They are active, schooling together, and otherwise healthy. I feed them API bottom feeder pellets and bloodworms on very rare occasions. They've never been interested in blanched cucumber, zucchini, lettuce, or cabbage really. I test parameters and things are normal, very similar to what is stated above. Bury the fella with their friend.
I go and buy 2 more panda cories from the same fish store, since I feel they're probably lonely without more friends. 6 cories now. No quarantine. Fish get ich and I raise temps to 82F. I know the fish can handle this temp as there was a heatwave recently and it was consistently 85F without issue. I dose with melafix, using slightly less than recommended because of labyrinth concerns. All of them recover. No issues.
Here, I had a friend's betta tank crack and I offer to house the fish in an emergency. It goes into my 10g with the cories and appears fine. However, during feeding i notice it gets aggressive but the cories are fast enough to escape. Next morning, I find a cory dead and it looks like it's been nipped. They rest with the others now. We get the replacement tank and the betta leaves my 10g. 5 fish left and an unfortunate scenario all around.
Few weeks later, find another dead. 4 left. The fish that died was part of the original 6, not the new set of 2. Buried in the garden. At this point, i've had 3 fish die unexpectedly and 1 from a bad situation. I don't believe it's bad luck now and something is wrong but I still can't figure it out.
A few days ago, which is 2 weeks from the last passing, I notice one fish's belly is swollen and its anus looks large/white. I dose with melafix and pimafix out of concern. Does not appear to get better but fish behaviour is normal.
Tonight, I find a cory dead. Given respects and buried with friends. It was not the cory with the previously described swollen stomach, it was a different one. However, seemingly overnight, all remaining 3 cories have abnormally large bellies as described earlier. They have been on melafix and pimafix these last few days.
It is here that I am lost and feel the need to ask for any advice or help. I feel awful for letting my fish pass. I cannot blame it on bad luck, as I feel there must be some underlying issue with such a pattern. I want nothing more than to ensure their safety.
As such, does anyone have suggestions on what to do next, or what the problem is? I can provide info as needed.
Here is my thought process on what it isn't. Let me know if any of these assumptions are incorrect or mistaken.
It is not dropsy or an external bacteria infection. Both pimafix and melafix are supposedly helpful for bacterial infections. There are no visible external symptoms. The fish die 1 by 1 not en masse, so likely not dropsy killing them all.
It is not water parameters. To my knowledge, the parameters are suitable for cories. I am diligent with water changes and vacuuming. After each death, i test the parameters and nothing is out of normal. The only variation is obviously nitrates, but they are always below 25ppm. Perhaps I misread my indicator, but it should still below 40 even being generous with the error range. Furthermore, the shrimp have been active, happy, and regularly molting. No issues. I figure shrimp are more sensitive to water, so they'd likely react to poor parameters before catfish, if not in tandem.
My guess is it is an internal parasite. Perhaps it would explain the bloating. My meds treat for bacterial and fungal infections, but not parasites. Parasites may be slower killers but can spread to other fish. This makes sense why fish are passing 1 at a time, not in groups. I will purchase parasite meds soon, but does anyone have recommendations? Else i will google a generic brand or see what is available at my lfs
If you have read all of this, I thank you for your time. I truly wish the best for these fish and any advice is appreciated. I will try my best to answer any questions.