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First the reef tank, and now two more!

This morning I decided to hit my "Fab 4" tanks: a bichir display, the Lake Malawi 55 gallon, the blind cave tetra exhibit, and the Congo tetra 29 gallon. Since the bichir tank is infested with duckweed, and the Congo tank is nicely planted, hence I don't want duckweed in THERE, I started with the Congos and worked my way back. Did my usual 50% water change on each tank (which is the usual amount I do every week), dechloring on the way, added Flourish to the Congos and Malawi and the bichir, and went to work on my saltwater queen angel exhibit.

While I was working on the angel tank, less than 30 minutes after I had finished the Fab 4, I stepped out to check over the newly cleaned tanks. The Congos were nowhere to be found; they had gathered in a tight corner near an air stone, and were gasping heavily. Lake Malawi was filled with gasping cichlids, and even as I watched, my dominant male ahli died. A few minutes later, the female went belly up.

Instant panic mode.

I dropped more air stones in both those tanks, pulled the dead fish, and waited; nothing new has happened yet.

I'm at a loss. The reef fiasco started a week ago, and the same reeffriend Greg, who advocated no more water changes and instead carbon use on the reef, told me that the freshwater tanks had copper poisoning from the copper water tubes that bring water into everywhere in the zoo. However, in the Congo tank, we have three bamboo shrimp; and they are fine and alive.

I wish I had water stats, but am home right now, and am seriously dreading what those two tanks will look like in the morning. What could have killed off two Malawian cichlids so fast, and stressed out the Congos...but left the bichir and all the blind cave tetras and their yoyo loach tankmate untouched?

pH shock perhaps? Perhaps a water source change has instigated a problem? (Random guess - I have had this happen - very not fun.)
Best,
Jen

H2S? Hydrogen sulfide is a poisonous chemical that can build up in water with no oxygen (like in a water supply system). It stinks (like rotten eggs).

It could be "anything".

--
Mats

I don't think it is H2S....someone did bring up the possibility of hot water coming out from the tap, but the water was cool to touch when I tested it after filling each tank.

if both the Reef- and freshwatertanks got in trouble; I'm fairly sure it's something in the water; all other symptoms and imbalances are a follow-up of the detoriation of the life in those tanks (like nitrates or ammonia, sick and dying animals)

Sometimes tapwater is not what it seems, you can have peaks of pesticides, heavymetal-poisoning, halogenes added (iodine, fluoride, chlorine), sudden pH changes you name it.

and usually the watercompanies keep shut about it, because poisoning drinking water gets them in a lot of lawsuits and so on.

but I think it's highly unlikely that all of your tanks suffer because of nothing; and the one thing those tanks have in common is waterchanges; I'd say there's the culprit.

I'm so sorry to read about this. Are these your home tanks or your work tanks? (I apologize if I'm not reading your post correctly.) If they're the work tanks, how close can the public get to them? Is there a chance others could have accidently dropped pennies in there or some other object? Just curious.

Call your local water company. I'd bet a beer they added Chloramines to your tap water supply to knock the bacterial counts down instead of adding more Chlorine (adding ammonia is cheaper than more Chlorine).
In the U.S., many municiple supplies do that now and then, most commonly in the spring and summer months.

Sorry to hear about your losses. In Ohio and Minnesota anyways, the suppliers do not have to notify you when they change the chemical mix in the tap water.

Minnesota was the worst (St. Louis Park and SE Minneapolis), for months, they'd run Chlorine only and everything is fine, then WHAM! Ever fish in the tank is suddenly gasping at the top of the tank.

If they added the Chloramines, you'll need to treat EVERY water change from here on out prior to use. There is no way to reliably detect it's presence or absence in your supply.

Give them a call and let me know if you owe me a beer. (that'd make two BTW, if you're keeping score!)

I was worried about the water as well, at first; but then I have done water changes on other tanks, and have suffered not a loss, including the discus tank, a queen angelfish tank, an electric eel tank, etc.

The reef tank incident happened a little over a week ago.

However, I think I may know what caused me to lose all but one Malawian cichlid and 6 Congo tetras. I use Flourish supplements in those two tanks.

I remember that I did use Flourish, the Carbon, the Iron, and the Comprehensive Supplement, on the tanks on Monday, and about a week ago, I read the Carbon's label. It mentioned that after a heavy water change to dose more carbon than the usual amount of 1 capful per 50 gallons. I had acted on this advice in the planted discus, rainbowfish, and killifish tank with no ill effects...but apparently in the cichlid and Congo tank, the effects were very ill, and I lost many fish, all of which were gasping at the surface, oxygen deprivation, I am positive.

I'm going back to my usual Flourish regiment. In some tiny good news, I did manage to find one sole survivor from the Lake Malawi Massacre, and only lost 6 Congo tetras. The bamboo and ghost shrimp in the Congo tank continue to do fine.

Do you have any idea if you've treated your water change with chloramine declorinator or just the normal chlorine declorinator.
There is a difference. Up here in Canada, the city where I am living treat our tab water with chloramine. Sometimes when people complain about fowl water from the tab, they will boost the dosage 2 or 3 times the normal amount.
If where you're living normally use chlorine to treat your tab, then they might have changed to using chloramine. More and more cities in North America are converting to chloramine because they are more stable and won't dissipate like chlorine does.
If your tanks is going through a cycle, then you know that something is very wrong in the tab water and your fish does sounds like they're going through ammonia poisoning.
Chloramine is a mixture of chlorine and ammonia, this prevents the chlorine from dissipating. When you declor the chlorine only, the ammonia is left behind and that will burn your fish gills and thus they can no longer breed and are left gasping for air at the surface.
There are chloramine test kits out there. Buy one and test your tab water.