Pygmy cories randomly dying off?

[Garbo Aquatics]

Hello all, I have a 10g planted tank with one very peaceful male betta, 13 ember tetras, some rilli shrimp, and now 6 pygmy cories.

Over the past few weeks I've been losing one or two cories a week, I cannot figure out why though. all fish are acting normal and the cories act fine until one will stay at the surface till it passes. I've also noticed the cories act completely normal throughout the day, it's only at night will one start to stay at the surface and die over night. The tank sits on my desk and I'm home all day so I constantly watch the fish and have not seen anything abnormal about the cories. 

When once surfaces it seems to be unable to keep it's self level and its head rises up, it will stick its fins out and breath rapidly, though it's not gasping for air. Bellies look fine, no pineconeing or bloat afaik, nor are they sunken in.

I drip acclimated the fish for about an hour, my lfs has a ph of 8.2 while mine is 7.7/7.8 so this is the only thing I can think of that might be killing them.

More info about the tank below.

 

The tank was established and fully cycled ( used old media) at the end of August. It's dirted with a sand cap (1/2in dirt 2in sand) filtered with a 20g coop sponge filter, and moderately planted. I feed crushed bug bites and algae wafers once a day, wafers go in once the lights go out.

Parameters have been normal since the first week, with only nitrate moving around 20ppm and 30ppm, ph is 7.7-7.8. temp is set at 78f and I change water once a week, about 25%-35%. 

Two weeks after setting up the tank I added the betta, one week after that I added 8 ember tetras, one more week and I add 6 cories, another week later and I add the final 5 tetras bringing the total to 11, another week passes and I add 5 more cories bringing the total to 11.

I understand the tank is overstocked on a bio load level, but params have been consistent for almost two months now, with only nitrates moving up to 30ppm/40ppm the day after adding new stock. They jump down after the first day or two.

 

During this time all fish are acting normal and eating, tetras are nice and red and the cories are always out looking for food. betta doesn't bother the other fish at all, only flaring when a bubble nest is made. Even the shrimp are berried and molt just fine. 

 

pics attached are of the tank and some of the cories, If I notice one staying at the surface I will try and get pictures of the gills and the fish in general. 

 

thank you for your help.

 

 

[Colu]

High levels of nitrates can effect fish's swim bladder causing buoyancy problems listlessness rapid breathing and can eventually kill your fish   you could have had a spike and  missed it some species are more sensitive to nirates @Garbo Aquatics

[Garbo Aquatics]

@Colu that would make sense, I'll start testing water daily and see if I notice anything jump. One thing I forgot to add was that I think the original 6 I got are doing well, hard to tell who is who but they have the most solid colors. I suspect it's the second group of 5 that I bought that aren't doing well, maybe a bad batch?

thank you for your help!

 

@Colu that would make sense, I'll start testing water daily and see if I notice anything jump. One thing I forgot to add was that I think the original 6 I got are doing well, hard to tell who is who but they have the most solid colors. I suspect it's the second group of 5 that I bought that aren't doing well, maybe a bad batch?

thank you for your help!

 

[Colu]

On 11/14/2022 at 7:41 PM, Garbo Aquatics said:

@Colu that would make sense, I'll start testing water daily and see if I notice anything jump. One thing I forgot to add was that I think the original 6 I got are doing well, hard to tell who is who but they have the most solid colors. I suspect it's the second group of 5 that I bought that aren't doing well, maybe a bad batch?

thank you for your help!

 

@Colu that would make sense, I'll start testing water daily and see if I notice anything jump. One thing I forgot to add was that I think the original 6 I got are doing well, hard to tell who is who but they have the most solid colors. I suspect it's the second group of 5 that I bought that aren't doing well, maybe a bad batch?

thank you for your help!

 

What I would do is monitor them closely for the next week test your nitrates just before a water change and then test after a water change to see we're It's wear your levels are I would aim for 20ppm  of nitrates if you notice any other symptoms let us know as it's also possible something else is going on