They're dead, Jim.

[B Considine]

All but 2 of the formosa in my 5.5 were dead this morning when I turned on the lights. Shrimp and snails seemed unaffected. Didn't have time to break out the test kits, so did a quick small water change. Only thing that I hadn't noticed before was so many snails. I thought I'd gotten the population down.

Are formosa prone to population crashes? Everything looked good last night.

Blaise

On the plus side, this looks like an opportunity to tear the tank down and start with something more interesting. Still, I always have a twinge of guilt when critters in my care snuff it.

[krisw]

Were you injected any CO2 into this tank?

[B Considine]

Nope. Excel daily and Flourish with water changes.

[krisw]

And no excessive Excel overdosing? If not, I'm clueless.

[B Considine]

I'm sure I've been overdosing regularly since I set the tank up in April. But until this morning, everything was chugging along fine. I culled a dozen last week to give to Donna for her tank at school, so I thought I'd decreased the bioload.

If the culprit is water quality, wouldn't the cherry shrimp have felt the effects first?

Blaise

[Ghazanfar Ghori]

If you see a bunch of snails out and didnt notice earlier, it may be due to some kind of stress that they're out and about.

Test the water.

[B Considine]

Will do.

I was planning on disassembling it and rescaping (if it can be called that) anyway.

It's just that this is the first time I've ever had a mass die-off in an established tank before.

May very well be bidding for new occupants in January, if not this weekend...

[B Considine]

Upon reflection, the only thing I've done recently is exchange a small heater (one of the pad type) for a small Aqueon 50 watt heater. Had my hand in the tank and didn't get shocked, so I don't think that's the issue. Haven't raised the temperature more than 2 degrees since the exchange.

[B Considine]

Took a water sample to SCALES last night. All parameters within normal limits. Slightly elevated ammonia and nitrites(?). Did a 90% water change and took the opportunity to reorganize. Found all shrimp, and 3 formosa (one of which was missing this morning).

While cause of the mass die-off is unknown, speculation was that poor circulation might have caused oxygen depletion.

[krisw]

Interesting.. Perhaps oxygen depletion but I suspect that giving the cooler time of year, and the fact that your tank is planted. One other thing popped into my mind that I've often wondered about. Given the dryer temperatures, have you used any hand lotion that might have ended up in the tank?