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Discussion Starter · #1 ·
Lost 4 fish (and possibly counting....) in the past 2 hours, so wanted to see if anyone has any clues. The tank is a planted/low tech 6 gallon Fluval Edge, setup for 2 months, otherwise had been doing fine. Has a soil substrate under gravel. had 2 corys and 4 harlequin rasboras since it was setup. Today I did several things (thus the confusion over what may have caused the catastrophe).

- I cleaned it a bit, had a bit of algae including bits of that slimy blue-green algae (was worse a few weeks ago, but even then, not a huge problem).
- Poked the gravel which released bubbles from the soil underneath. (this has happened before as well, just stuff decomposing down there presumably).
- Added some Seachem Excel. (thought might jazz up plant growth - they're ok, but not thriving).
- I added a rock - white quartz with veins in it. Will try to attach a pic. I do not recall where I got this. Probably a LFS, but its possible not....
- Went to LFS 2 hours later, and bought 2 more harlequin rasboras, and a small platy.
- Acclimatized & added fish via netting. No LFS tank water went into my tank, except that on the fish's body.

- 2 hours after fish added, one cory was 'playing' dead, which was new with these guys, although I'd seen it in my other tank shortly before said corys ended up dead.
- An hour later, two of the rasboras were not looking good - on their sides, or near the top.
- An hour later, four rasboras and the two corys were dead. Not clear if the 4 rasboras were the old ones (which had been perfectly fine), or 2 old plus the 2 new.
- ph is high, but had not changed appreciably before and after this. 7.8 - 8.0 or somewhere in there.

I then did a 75% water change, removed the rock, and am seeing how things go. Two remaining rasboras do not look great (faded) but have not gone sideways. Platy is lying low. If their condition degrades at all, I'll throw them in a 30g tank I have that has no problems.

Theories:

1. The piece of quartz (perhaps the veins in it) had something toxic in it. Or perhaps some cleaning chemicals on it. I may not have rinsed it thoroughly enough. This is my leading candidate.
2. My hands had some residual soap under the nails or something that got in the water.
3. Bubbles from the substrate were rather toxic (but I've had them come up before, whenever I poke at the substrate).
4. Something else I'm not thinking of....

I've always found keeping corys in my tanks is near impossible, but these two had lived 2 months in this new tank and seemed fine. In my 30g tank, which has a lower ph (low 7's I think; its much more established and heavily planted), I can never keep them alive for more than a month (of the 3 I got when I got the 2 for the Edge tank, only 1 survives). They look fine until the moment they die. Even then they look totally fine - not pale/discolored, nor skinny, nor nipped at. The only thing I've noticed in some cases (not today) is small reddish patches on/under their skin in places.

Any suggestions are welcome! I'm mostly posting to see if its obvious to anyone that that rock is a big no-no for a tank. I figured quartz is quite inert, but again dont know about the veins, and dont remember where I picked it up, although LFS is definitely very possible. not sure what else would have wreaked such havoc in so little time. Although I did not notice anything wrong with anyone when I added the new fish, and that was at least 2 hours after the quartz went in.
 

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Your guess about the rock is probably right. Sorry you had this problem! I added a quartz-veined rock from a river in NC to a tank where I'd had some large fancy goldfish for years. I boiled the rock first and also tested it with vinegar.
It slowly killed off my fish anyway. They leach something into the water IMO. No more pretty rocks for me!
 

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That veining might be some mineral that it too much, too concentrated in that small tank.
The bubbles in the substrate... smell them. If they smell bad, this is bad news. If you cannot smell anything more than a healthy tank smell, that is OK.
Some forms of blue green algae can release toxins when you disturb it. In a larger tank a small amount might not be a problem, but in a 6 gallon there is not a lot of water to dilute these toxins. To clean this stuff, I would have a siphon going and aim it right at the BGA you are scraping off so that it immediately is removed from the tank.
Residual soap or other stuff from your hands is always a possibility.
Did you dose the Excel properly?

I am more concerned that Cories do not live long in any of your set ups. Which species have you tried? There are several Cories that are quite tolerant of a very wide range of pH, though they prefer softer water. The more delicate species generally need the low pH, soft water, though not as extreme as some fish.
Most Cories are relatively cool water fish, temperature into the upper 60s for a few species, and through the mid 70s for most. A few are OK in warmer water.
Do you always get the Cories from the same source?
 

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Discussion Starter · #4 ·
Update: the new fish have all survived (2 rasboras, and the platy).

So I'm now thinking it was probably the Excel. Someone pointed out on another site that its toxic if overdosed, and I probably overdosed it (and I didnt read the bottle...). Since it was several years old, I figured it had probably lost its potency anyways, so put in more than I should have as I wanted to empty/toss the bottle. Bad choice!

I may put the rock back in this weekend while I'm home and watching. Any sign of distress and I'll act immediately.

The bubbles do not smell bad, so hopefully they are nothing to worry about. I've put my nose down to the tank when poking the substrate, and really dont smell anything different, certainly not noxious.

There was more BGA than I'd thought, a thin coat coating most of the leaves on the various crypts and a microsword. I had wiped the worst off with my fingers in my initial cleaning, so that plus the excel might have been too much. Am hoping the BGA is just part of a new- tank syndrome and wont recur substantially.

Thx for the info on cories - I've tried a few types (sticking to the less expensive varieties for obvious reasons): most recently albinos (none survived long), and currently jullis, which seemed to be working out better until my incident. The pH is high, the water is hard (I've given up trying to fight that with additives), so maybe they're just not tolerant of DC water. And summers, the temp is definitely in the upper 70s or at times low 80s if I want to keep the lights on. I get them from a local shop I've trusted, not a chain.

I read somewhere that you want to get wild-caught cories, as they will be more robust than locally bred. I wonder how much truth is in that. I'd frankly much rather use locally bred fish than encourage harvesting from the wild. Although I've no idea if freshwater aquarium fish harvesting is a problem like saltwater is or can be...anyways, I'll ask the LFS next time about origins in case they know.
 

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Albinos are hatchery raised, and might be any of several species:
Bronze (C. aeneus) or Pepper (C. paleatus) are the two that I remember. These are both reasonably durable species, though the Pepper comes from cooler water.

Many other Cories are also tank raised, a lot of them in Florida. I am not sure if Cories are one of those that are better wild-caught or tank raised. In general I think tank raised are better up to a point. They are often bred in harder water, so are better adapted to that, but if the parent stock consists of too-few individuals then tank or hatchery raised stock can get in-bred. A conscientious breeder will out breed often enough to prevent this.

Planet Catfish is a good source of info about Cories and other catfish.

Perhaps put the rock in a bucket with water drained out of the tank for a water change, and add just one fish.
 

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Yes, overdosing of Excel can kill your fishes but it's more likely to kill shrimps, algae and plants first. Try sniffing on Excel and you'll understand why it can kill...hahaha (actually please don't try the stunt). I did it by accident when tried to peeped inside the bottle and got my eyes hurt for a few seconds - curiosity almost killed the man :D
 
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