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Quarantine Tank set up on Friday, February 10th.
Tank: 20 gallon long
Water: Bottled Spring Water
Substrate: white sand (bought at LFS for freshwater tank, I rinsed it well).
Decorations: Two Sphinx and Egyptian pillar and one medium river rock (was boiled)
Water Temp: 78F to 80F

Tests (after set up and before fish) 2-12-06:
pH - 7.6
Ammonia - 0 ppm
Nitrite - 0 ppm
Nitrate - 0 ppm

Tests today 2-20-06:
pH - 8.0
Ammonia - 0.50 to 1.0ppm (I know that's not good)
Nitrite - 0 ppm
Nitrate - 0 ppm

I've lost four of seven Spotted Cory's, one of two Sterbai Cory's and I still have the three Bronze Cory's. The Spotted and Bronze Cory's are from the LFS and the Sterbai are from an online aquaria place. I ordered four Sterbai but only two arrived alive, one died two days later and one is still alive and kicking.

I will do a water change to help with the Ammonia and pH. I didn't know pH would rise like that.

Any thoughts on what I'm doing wrong and/or ideas as how to keep the other Cory's alive?
Thanks.

The ammonia level rose so high because you tank is not cycled. It takes at least three weeks of running to acheive the appropriate levels of benefical bacteria required. Then you add fish slowly to build up the bio load. If you have another aquarium running seed the tank with filter material from it to help get the bacteria into place.
As for the rise in pH there are a number of factors playing here. Bottled spring water, at least here in Canada, is high in sodium, this would add to the kH in the water which affects the buffering of the water.
The rock may well be dissolving in the water, you don't state what type it is, and with a high kH the ph will rise.
Also your water is out gasing CO2 as it sits in the aquarium. This always leads to a rise in Ph. If you can get your hand on reverse osmosis, you can try diluting the aqaurium water to lower the kH.

I hope this helps.

Jeff

The Spring Water I'm using is Sodium Free and the Colorado River Rock is the same kind of rock I'm using in my 75 gallon (about 25 of them) with no problems.
I use the same water in my ten gallon (for about five months now) and it has never gone through cycling. I empty about 1/2 the water out every month and the readings are great. I have two betta's in that tank. Do you think the reason ammonia is showing up is because instead of rinsing the sand in spring or R/O water I used tap water? My tap water has a 1.0 to 2.0ppm Ammonia reading? I did add Prime to try to take care of it though. I thought Cory Cat's were supposed to be pretty easy. They are a lot harder than my Oscar's and Betta's. Thanks for responding. I really do appreciate it.