Fish Keep Dying 3-4 Weeks - Could Tetras Be To Blame?

califus

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Alright so I have a ~2 year old heavily planted tank (water parameter are all perfect they've been stable for the entire life of the tank since fishless cycle and I have had them checked, re-checked, checked at home, and at multiple LFS' since I started to lose fish).

15gal tall with an aqua clear HOB filter, sponge and double biological filter.

I have 7 green neons that I have had for the entire life of the tank, they were the very first fish I added. They seem perfectly healthy. However for the past year or so, any new fish I attempt to add to the tank start dying off after about 3 weeks, some maybe make it 5, but they all go. Some of the first few that were "originals" with my neons that had been added in the first few months I had the tank set up (a dwarf gourami, 2 platys, corydoras) did live for a few months before they died, looked like it was almost swim bladder as they were kind of sinking - I tried the peas etc but they all went. I didn't think anything of it, really. Then I starting losing all other fish that I tried to add, and they all went about ~3 weeks after being added. I did have cyanobacteria about 6 months ago which I thought may have been starting when I had added some of the fish that died - but I took care of it with erythromycin and waited several months to make sure everything was good - neons never seemed affected at all.

Recently I added 6 espei rasboras. Found one dead this morning, and it's been about 3-4 weeks (the usual timeframe I lose the fish). I just know the rest will follow.

My only assumption is that maybe these darn green neons are harbouring some kind of disease they are immune to, but kills everything else. The espei don't seem to have physical signs but the last two feedings, two of them didn't come to eat and were kind of hiding so I was getting worried. But I didn't see any swim bladdery or other obvious symptoms like gasping, etc. Just did a water change this morning and one looks like its swimming a little erratically (darting all over the place) but that may just be from me disturbing them, I don't know.

I don't know if it's relevant but I got a new stronger LED light maybe 6 or 8 weeks ago and after I added it my neons seemed to be hiding all the time - I assumed it was the new stronger light. I added the rasboras to see if that might help draw them out and it did. They all dither about together and aren't schooling or seeming frightened or anything.

What is happening?! Can I save my remaining rasboras?
 

Floundering_Around

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Do you quarantine your fish? Rather than your green neons harboring a disease, it's probably your new fish that are carrying diseases from the pet store. I'm not quite sure what you can do if the dying fish don't have any noticeable signs before dying (other than running meds through the whole tank to TRY and kill off whatever is affecting them).
Try feeding high quality fresh and frozen foods to help them fight off whatever "it" is
 

Ollie_Blue_Aquatics

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I don’t think that tetras have the ability to kill something like a gourami in my experience it is usually the other way around and I don’t believe that these fish actually live in the regions of the tank that the tetras do other than the platies
 
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califus

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Hey, so I've got 0 ammonia, 0 nitrites, and 10-20 nitrate depending on the time of the week. Temp is a solid 25 degrees. Water is tested all the time, daily if fish are dying on me, weekly otherwise, never had a variation (except immediately after a water change as this raises the ammonia slightly our tap water is 1ppm).

pH is 7.4 right now it looks like, and all the LFS run off tap water too so it's not going to be a pH acclimatization issue from them to me. One of the stores did suggest it could be pH changes overnight due to lack of oxygen at night in a planted tank and suggested I test the pH at the very end of the day before the lights go off, and early morning before they turn on, which I am going to do tonight - although the other fish store said that was nonsense as my tank is over filtered and has a ton of surface agitation.

I do not change my filter media, but I rinse it every few water changes in the discarded tank water. I do water changes of 10-15% weekly.

I don't have a quarantine tank as this thing is only just barely big enough to be a quarantine tank itself and it was kind of my "beginner" tank that I've learned with. I am going to be setting up a 55gal once this is all sorted and then I will use the current tank as one.

I basically just do the old float the bag and slowly add small amounts of water over a period of time, then net them out and add. My water tests literally the exact same as my LFS so they said there shouldn't be any real issue with this (other than having sick fish obvs). If it were some sort of shock or water change difference wouldn't I be seeing death or stress a lot sooner than 3-4 weeks?

I took my dead fish to my crazy fish guy at the LFS (honestly he has never steered me wrong he's crazy knowledgable). He looked at it under a microscope and couldn't see anything other than a few very small "lesions" which he thinks is a parasite, but doesn't know which one, or why/how my neons might be hosting them but not dying from them. There was also a doctor of biology there who is a fish enthusiast and he wasn't 100% sure either but said parasite sounds about right, could have a 3 week incubating period and be internal. He also offered to take my next dead fish to the lab to investigate for free which would be pretty darn cool, but I'd rather not have more die.

The current plan is to treat with Paraguard but I have to move my inverts to my sister's little desk top tank that only has a snail in it. Hopefully, if it is a parasite (which I don't really have any way to confirm) my inverts can come home after 2-3 weeks.

Ugh. I don't even know how to catch these shrimp in a planted tank with tons of shelter. Let me know if any tips on that!
 

TexasDomer

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It could be a parasite, but it could also be a lot of other things (bacterial, viral, etc.). It's also possible they're coming from the store sick, rather than getting something from your neons.

How are they doing?
 
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califus

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I just stuck it out instead of tearing the tank apart and setting up a quarantine or treating with anything. I figured either I was going to lose the rasboras, or my snails and shrimp, or both, so why mess with things I don't understand. 1/5 of the remaining rasboras remained "sick" - really pale, didn't eat for almost two weeks that I could see, but was still kicking it somehow, sometimes hanging out with the others but usually going to hide at feeding time or if I came up to the tank. I finally caught him and took him out today, took him to the fish guy to give to the lab. He also said he hasn't lost any of the rasboras from the same batch. I felt terrible, taking him in alive like that but I need to know what's going on in the tank so I don't poison a bunch of other tanks with whatever is going on in there (my shrimp are breeding and I was planning to put some in my new tank - now I don't know). There's nothing visible at all on the fish other than it being almost a pale pearly translucent (instead of shiny gold like the remaining 4), and skinny.

It's a pretty heavily planted tank, so I had to mess about for a bit to catch the fish. I may have stressed the others - the 4 remaining fish aren't out and about like usual tonight but I'm really hoping this ordeal is over. They ate well today and are maybe 4+ weeks in the tank now so... fingers crossed. Either that or they'll keep dropping one by one

If anyone knows what that sounds like, I would love to know.
 
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