Just call me Fish Killer, Terror of Guppies

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Purple_drazi try not to get discouraged, I also think that panda cories are very delicated fish. I have a bunch, but about one a month dies. I even have them in different tanks

Odd... am I the only one with hardy Panda Corys? I've only lost 1 over the last 3 years. My aquarium conditions during summer months are pretty brutal. The temperature is between 86-90 degrees, with higher than normal nitrate (20-40 mg/L) due to slowing plant growth.

 

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If your tapwater is ok, then you could try to make bigger water change. Maybe there too much phosphates in the water...

I've never heard of any fish dying due to excessive phosphate. If this were the case, products like pH down will wipe out most fish due to massive amount of phosphate (in form of phosphoric acid) they release in to water.

 

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What is the ph of the store where you are getting fish from to the ph of your tank.

It's highly unlikely that pH is killing them. pH shock, or shock of any kind for that matter, kills within several hours, not weeks. Fish and plants easily adapts to higher or lower pH in several weeks.