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I seem to recall that the sign at Pet Smart did have a different species listed than corydoras for the emerald green "corys" that I purchased. I forgot to write it down when I bought them and was going to go back when I got a chance to get it. I do remember the sign saying that they reached 4", which was larger than the other corys they had, and was one of the reasons I went with them (they also looked better than anything else). It didn't occur to me that they weren't really corys, but as long as they get along I guess it isn't that big a deal.

I realize that I can get a water analysis from the water department, but that is taken at the source. It doesn't account for anything in the pipes along the way to my house or anything in the pipes within the house. I have all your standard freshwater test kits - Gh, Kh, nitrite/nitrate, ammonia, phosphate, etc - but I'm more interested in things like metals and other chemicals.

I would write this off as a bad batch of corys if it hadn't happened with previous batches with almost the same symptoms/reactions. I have to believe something in my 150 is detrimental to cory health. I'm just struggling to figure out what.

David

Well, so if you spend $150 to find out that your local water contains something harmfull (assuming it's as easy as that) - what do you do then? I think getting RO-filter is a more cost effective solution, as that WILL solve the problem...

And more importantly, what if there ISN'T anything showing up in your test-sample?

I know this may sound cruel to some of you, but I would suggest that you take one or two of your known healthy cory's in a couple of weeks, and subject it to living in the 150g tank for a little while. If it keels over, we know it's not the fish, because the others of the sample group are supposedly still alive.

The next step would be to introduce a large water change from your tap-water to your "clean water" tank and see if that affects the fish as well - if so, put them back on drinking water by a large water change back - that should make them OK again, I should think.

However, I'm pretty sure it's not any metal compound in your water - unless it's so bad that you can see it (assuming it's copper, iron, etc), it's unlikely to kill the fish almost instantly. Most of us here in the UK have copper pipes, and that's not a problem. Lead pipes come into my house at the moment [plan for replacement at some point]. I use plain tap-water for my fish, and they don't seem to mind.

If there's pesticides in your water, then it's not coming from the pipes on the way, it's from the water supplier.

I can't think of anything that would come from normally used water pipes that would poison fish that are known to relatively hardy within days/weeks.

I'm not saying you can't send off a water sample to some company for testing, as it is your money- but I'm somehow doubting that it's well-spent money. You can, as I described above, figure out if it's the water or the tank (with some risk to the fish involved, unfortunately).

I'm pretty sure your new fish are - they are what it should be if they are called "Emerald cory" - they are indeed in the same family, just not the same genus.

--
Mats

The RO/DI is the ultimate soloution to producing pure water
There may be a much simpler solvable problem going on in your 150. It may be that it is just taking awhile to become fully cycled as there really is nothing written that it always takes X amount of time, just general guide lines.
The most common source of after treatment plant occurrence of heavy metals can happen in US water supply. Sometimes the hotwater tank adds metal ions and fresh soldered copper pipe that have not be flushed prior to use is the another possibility. Those are rarely a problem and if you use any of the common water conditioners they also are designed to chelate free metal ions to add an extra level of protection.
I think you will find that the 150 will support your Corys as well as any other fish without doing anything except continued good maintenance practices in due time.
When it comes right down to numbers, only a few per cent of all American aquarists use RO water and most of those are reef aquarists. The rest of us get by without them. I own one but rarely use it. I raise discus, Corys, bushyNoses and very many other species from diverse origins. I raise fish for sale to retail shops in my region. I use RO water when I'm trying to breed something like a neon tetra because their eggs won't hatch in water unless it is almost pure and a little acidic.

I had thought about adding tap water to the 10 gal with say a 50% water change to see what happened, but haven't decided if I want to try it yet. I guess I could do another big water change with bottled water if I start to see issues. I agree that it's not likely something in the water is causing the problem, but without a detailed test it can't be ruled out definitively. If the test comes back normal then I've ruled out the water source as the problem - I don't need an RO unit at that point.

I stumbled upon what looks pretty darn close to the corys I purchased in the cat-elog. The c. melanotaenia (elongate bronze cory) looks like what I have. I'm not sure if the bronze coloration is all along the bottom on mine, but it's close. The cat-elog shows a pretty low water temp for these guys 68-73F and my tanks are at 77-78. Breeding shows not known so they were more than likely wild caught. So it seems tank temp could be an issue. I may lower the temp a bit and see if that helps them.

David

First off. Source of the Fish. You said you buy fish from Pet Smart. Did any of these batches come from there? I would send anyone anywhere but (insert generic chain pet store name here). I have yet to see truly healthy fish come out of them. To me if you want to buy unhealthy fish with high mortality that is where you go. I have seen some nasty stuff come from them and their central filtration systems (another pet peeve). I am going to bet if that is the source or another with central filtration your problem is you repeatedly purchased doomed fish to begin with. Wholesale sources are another factor...

To me if that is not the case and from my very humble experience... I am going to say it has something to do with "PH shock". 6.9 is starting to go in the low end of things. Forget about trace elements and minerals in the water for now - that normally takes a good amount of time. Many fish are more susceptible to damage this way then from temperature changes. Remember pH is on a logarithmic scale so if the store has a pH of 7.8 or 7.9 (pretty typical - I can't say about your local though) and you drop them into 6.9 water that is quite a shock. What is your tap water pH?

I have read a lot of articles on the subject and the suggestion seems to be no more then half a degree change in a day as recommended guideline. So no more then .5 degrees. I am not saying I haven't changed water pH by 1.5 in a few hours on fish before because I have. But I personally think corys are kind of delicate to shocks. I have had and kept them on and off for quite a while. Presently I have a breeding group of Sterbai and am growing out an Albino Aneaus group. The more I think about it cory cats are really kind of touchy. But I do have to think that if something was seriously wrong with your water it would affect all your fish and not just them.

More water thoughts... Do you KNOW the water source for both your local and that of the store? Just because you are in the same county does not mean it's the same one. I can think of 4 different public water sources in the county I live in. There 3 small ones for small suburbs and the main one feeds two cities and about a dozen suburbs. The water that comes from the main Water plant also varies greatly from location to location. Some of the more remote suburbs you can smell the chlorine coming out of the water as soon as you turn on the tap. Each water tower or pumping station acts as sort of an "water alteration" point - add chemicals to keep the water safe.

What fertilizers are you using in your water? I have not had any problems with either group of mine and the use of fertilizers - that I am aware of. (You might have mentioned but I sort of skimmed the later parts.) Both my groups are in heavily planted tanks...

Are the corys bloated at all when or just before they die? (Indicating internal organ failure and/or sepsis.)

Good luck...

None of the batches that have had issues came from Pet Smart. In fact, the ONLY fish I've ever bought at Pet Smart were the brochis "corys" I mentioned in this thread. The batches with issues have come from what I consider reputable fish stores. One batch came from "The Fish Store", which is probably the best fish store in the Atlanta area.

I did not do an analysis on the water the fish come in from the store so I don't know the parameters. That may be something to do in the future. I can say that other fish bought at the same time have done fine.

I fertilize the tank with potassium nitrate for nitrate, something (forget the substance off the top of my head) for phosphate, potassium sulfate for potassium, and flouish for micros.

I do not believe I have been getting good water movement in the tank, especially on the bottom. I'm in the process of trying some things to improve the situation. I do not know if that could have contributed to the issue or not. Maybe the bottom of the tank stagnates somehow. The plecos don't seem to mind, though.

The 10 are still alive in the 10 gallon. The original 2 I pulled out of the big tank still don't look 100%, but they're hanging in there. The brochis guys look good. I haven't tried adding tap water to the tank yet, though I need to do a water change and may use a 50/50 tap/bottle combination for the refill to see what happens. I'm just happy they're still alive at this point and don't want to rock the boat just yet.

David