Why does svery Tetra I buy die and all my other fish live? Help!

[TreeFiddyB]

Hi everyone!

I'm a first time aquarium owner and am absolutely lovin' it! I never knew how involved and addicting it could be and let me tell you; I'm hooked!

I'm writing this post today b/c I have an issue that I absolutely cannot solve. I've put in probably 10 hours online, spoken with 3 pet store employees, and have consulted with friends who own tanks... and no one has an answer. I'm hoping someone here has maybe come across this same issue before and can help me solve it.

My setup is;

55 gal tank/Freshwater/Aqueon Quietflow 75 filter/2 Tetra Whisper 40 Air Pumps/Temp 77-78°F

My issue is;

Until 6 weeks ago I had a healthy, happy, vibrant little aquatic ecosystem going. It's a Glofish setup and included the following fish;

8 GloTetras
4 GloDanios
4 GloSharks
1 GloBetta
4 Cardinal Tetras

6 weeks ago I decided to do a deeper clean... up to that point I had only ever vacuumed it and used a scrubber to wipe clean the inside glass. But a lot of brown algae was growing and covering everything so I decided to give the tank and decor a little deeper clean.

Regrettably I took the advice of a friend and did a 50% change. I also put the decor in a bleach bath for 10 minutes (I did a 20 to 1 ratio with the bleach. I know they say 10 to 1 is safe, but 10 just felt like a lot to me.) Then, with half the water out I gave the substrate a real good vacuuming and wiped everything with with a washcloth and warm water. Finally, I put everything back in place and added water that I had preset at 76°F.

That night before bed I did a water check with an EZ strip and everything showed as being in the range of normal so I went to bed.

The next morning I woke up to find 7 fish had died. All the Cardinal Tetras were gone as well as 3 GloTetras. Then the day after that, the remaining 5 GloTetras died. Luckily, the Sharks, Danios, and Betta survived.

After that I was super cautious and I started checking the levels twice daily with the Master Kit. I did that for the next month and except for a slightly higher the pH than normal everything else has been great.

I've been very consistently at;

pH: 7.4
High pH: 7.8
Ammonia: 0
Nitrites: 0
Nitrates: 0

After 4 weeks of testing the water and seeing the previous occupants looking so healthy and happy I decided it was time to add some new friends back into the fold. So I purchased, tempered, and added 4 new GloTetras and 2 new GloDanios. Everything seemed fine when I went to bed... the next morning however, all 4 Tetras were dead... the Danios were fine.

So after that I changed 7.5 gallons and kept checking on it. I assumed the Tetras maybe died because it hadn't re-cycled enough. After two weeks and all was well I figured it CAN'T still be bad. So I got just 1 GloTetra, 2 neons, a guppy, and another GloShark. The next day - everyone was fine! But the next day after that, the GloTetra and Neon Tetras died, while the guppy and Shark were perfectly fine (and all the previous fish).

So for now I'm not buying ANY more fish of ANY kind. But I desperately want to know why my tank is killing Tetras and only Tetras! I just can't figure it out! Why is it that one specific line of fish is dying but no one else? Oh and also, it just so happened that my 3 fish purchases were at 3 different stores so it's not likely to be a bad supply or bad management. I'm completely at a lost.

If anyone has an idea please let me know!

(Oh also... one of the numerous things I've learned along the way is that just because someone has a fish tank setup in their house, that does NOT mean they necessarily know what they're talking about LOL! Uggh.)

[libertybelle]

Yeah to that last note... definitely true.

First of all as to only losing one type of fish and not others, could indicate that your water parameters were not ideal for this species or that species is more sensitive than others. If water parameters are not quite ideal it could make them more likely to be pushed too far by something going wrong that they may have been able to survive otherwise.

The reason I bring this up is because if your ph is really as high as 7.8 that could be not ideal for the tetras. Most tetras including neons prefer soft / acidic water. (Do you have a gh/ kh test kit or strips that will give you approximations of those numbers too?). If they’re already a little stressed from the ph another stresser like a large water change or mini cycle could be more likely to put them over the edge than something like a danio or guppy which are extremely hardy and adaptable. That said tetras may not breed at 7.8 but they can usually adapt. You may want to find out what the ph of the water any tetras are coming from is. If it is quite a bit lower you would need to allow them to adjust slowly by a drip acclimation over a longer period of time than if the store ph is similar to yours.

(Ps don’t buy ph down. If you do choose to adjust ph there are more gradual and natural ways that are way better for fish than ph down)

Have you ever seen nitrates in your tank? Is it heavily planted? Trying to figure out who you are seeing no nitrates with a decently stocked tank. When you use the nitrate test do you shake bottle 2 like crazy? If not it could be you do have nitrates but the test didn’t work due to not shaking well. It’s notorious for that.

Did you rinse any beached items (including your hands) with dechlorinated water with extra dechlorinator? I suspect trace bleach would have killed everything but gotta ask!

My suspicion is two fold. Ph naturally drops in a tank over time especially if there are things like driftwood in the tank. A 50% water change plus “deep clean” is a risk on two fronts, first: the water you are adding in are different parameters than your tank and so may swing ph/gh/kh. Can also trigger a mini cycle and transient ammonia/nitrite. Either of those could have caused the initial die off.

Having trouble with new fish could just be them needing a longer acclimation to a higher ph.

You could check your tap pH and compare it to your tank pH to see if that could be a source of stress during larger water changes.

[charliebankston]

Yeah, cardinal and neon tetras , like liberty said, are low ph blackwater fish. A little more sensitive to water parameters. And all that brown, slimy gunk in your filter is the beneficial nitrifying bacteria. A deep cleaning in it and your decor with bleach water prob killed all your BB and started your tank cycling again. And those neon and cardinal tetras won't survive a cycling tank. Zebra danios on the other hand are one of the best fish for doing a fish-in cycle