Dead fish - Need advice

[Okesa]

The school I work at has a planted community tank. There had been 4 albino corydoras, 4 cardinal tetras, some amano shrimp, and 2 nerite snails living in the tank for just over a year with no problems. Last Wednesday we added a few more amano shrimp to help with algae control. Last Friday when I left for the weekend, everything was fine. On Monday, all the fish were dead, but the shrimp and snails are all fine. I checked the water parameters immediately upon discovering the dead fish, and nothing seemed obviously wrong. The water temp was 28 C. Before we get any new fish, I want to make sure that the tank is ok. Right now my only theory is that the water got too hot over the weekend. However, the fish survived last summer without any issues. Does anyone have any ideas as to potential causes?

[Fish Folk]

I am not familiar with the Tetra test strips. If known, can you please estimate the values for:

pH

KH

GH

NH3

NO2-

NO3-

 

What's the aquarium size?

Might someone have added a contaminant to the tank? Might someone have had something caustic on their hands when adding new shrimp?

Did the Electricity go off for any period of time over the weekend?

What kind of filtration are you running?

Is there any stray current in the aquarium?

What was fed over or just before the weekend?

[Okesa]

NO3 - between 10 and 25

NO2 - around 1

GH - between 4 and 8

KH - between 3 and 6

PH - between 6.8 and 7

CL2 - 0

NH3 isn't tested on these strips

Aquarium size is 10 gallons.

No one was at the school to add anything to the tank over the weekend, and the shrimp were added with clean hands and a net.

As far as I know, there weren't any electrical outages over the weekend.

The tank has a sponge filter.

I don't *think* there is any stray current in the aquarium. How would I be able to check that?

The aquarium has an automatic feeder. The food is this one for small and medium sized fish by Hikari. 

[NathJK]

It has to be something that would kill everything so my guess would be ammonia, but it's just a guess without testing. Seems pretty likely though in a school tank that's small over a weekend. Doesn't take much to do in a whole tank. 

[Okesa]

Would the amano shrimp and nerite snails be less susceptible to an ammonia spike? They are all still happy as can be.  

[Patrick_G]

I’m sorry this happened, do you have any idea how hot it was over the weekend? 

 The NO2 seems high, it should be zero. I’d be interested to see how much NH3 is present. Both are toxic to fish and could be the cause of the deaths. It could be also be something else. 

[Okesa]

I am not sure how hot it got inside over the weekend, but there are tanks in other rooms of the school that theoretically would have reached the same temperature and didn't have any issues. The outside temperature was definitely over 30 C. The fish survived all of last summer with no problems, but this year we are having an early heat wave, so heat was one of the first possibilities that came to mind.

I'm planning to get some ammonia test strips since that seems to be the only major thing not included on the tetra strips I already have. I also found a product called Seachem Ammonia Alert. If anyone has used it and knows if it works well, I'd appreciate the feedback.

After I did the test strip on the aquarium I removed all the dead fish and did a 50% water change, so the NO2 should hopefully have gone down, but I need to do another test to confirm. 

(On a  completely different note, @Patrick_G your planted tank looks amazing!)

[nabokovfan87]

I think your assumption about temperature makes a lot of sense.

Did the shrimp have issues and look "cooked"?  Does the tank have a lid or is there some way to keep the tank lower (if desired to do so)?

On 7/6/2022 at 7:16 PM, Okesa said:

I'm planning to get some ammonia test strips since that seems to be the only major thing not included on the tetra strips I already have. I also found a product called Seachem Ammonia Alert. If anyone has used it and knows if it works well, I'd appreciate the feedback.

I have seen it, haven't used it, but it's basically just something to give you a constant reading.  I would recommend using the strips.

[Okesa]

@nabokovfan87 - the shrimp are all still alive. Only the fish died. That is why I'm so confused about what exactly happened. 

[nabokovfan87]

On 7/6/2022 at 8:33 PM, Okesa said:

@nabokovfan87 - the shrimp are all still alive. Only the fish died. That is why I'm so confused about what exactly happened. 

Agreed, that is peculiar. Especially with amanos.  Potentially the corys were more sensitive than the amanos. 

Needless to say, if the tank has a heater, I'd verify it's working properly.  I'd verify temperature in some way as well if you're using one of the glass thermometers (sometimes the little paper inside can move).

I recently had an issue in my personal tank where amanos were stressed.  I asked on the forums regarding the issue and they showed signs of redness.  If you see some redness (shell color) compared to the normal black or clear coloration, I would note that here as well. If you don't, that's a good sign.

Is it possible there was a power failure and filtration stopped?  I have had corys survive an extended power outage.

[Okesa]

The tank does have a heater. I unplugged it after I noticed the dead fish, but (assuming the thermometer is accurate) the temperature hasn't really changed, which makes me think that it wasn't malfunctioning. When I get the chance I'll pull it out and test it in a bucket or something to make sure it is definitely working correctly. 

I *think* my shrimp are looking clear/black, but I will check on them again this afternoon when the students have gone home. 

As far as I know, there weren't any power outages over the weekend, but because there wasn't anyone at the school I don't have a way to verify.