Need help with corys please!

[hollyval]

I love corys but can't seem to keep them. I have lost 3 pair over the course of the last several months. All of my other fish(lemon tetras, danios, clown loaches, tiger barbs, swords) are fine. My tank is established with zero ammonia and nitrites and nitrates staying at about 20. I do have super high (8.0+) ph. I tried with no results to bring it down with PH down but was advised it was better to just leave it alone and while my corys wouldn't breed in such high ph they could live just fine.
I feed a little extra food to make sure some gets to the bottom and also drop in sinking pellets when I turn out the lights. I never see them eat and I hope they aren't starving.
My only other guess is that because I have a 46g corner tank that maybe it is too deep for good oxygen at the bottom. I tried to add a bubble rock at the bottom to see if they congregated around it and they never paid any attention to it.
After a few days of being in my tank they stop working on the bottom and just lay around. Then they spend all their time hovering around the top of the aquarium and finally they die. I am at a total loss here. I really want to keep them but I don't want to be responsible for any more deaths. Do you think it could be high ph, not enough food or not enough oxygen? Do you have any other ideas? Thanks in advance for any help.
Hollyval

 

[PumaWard]

How do you acclimate the fish to the tank?

I used to never be able to keep cories for more than a few weeks. At the time, I would only let the temperature in the bag and the tank become equal, then I would release them.

I stopped having problems (and haven't lost a cory since) was when I added a cupful of my tank water to the bag every 5-10 min for 1/2 and hour or better.


HTH

 

[Hound]

Its possible they aren't getting enough food. Clown loaches are probably quite a bit bigger than the corys. I find that my corys eat with lights on if I stay relatively still in the room. I also can't remember how tall a 46g corner tank would be, but I know it took a bit for my peppered corys to start sufacing for airbubbles in my 50g tank. For the first 30 mins at least one or more would swim up about 12 inches and dart back down . That was at a time when they were the only fish in the tank. With other fish present they may not want to surface in a deeper tank if they are too nervous. Can't remember to be certain, but I believe all corys need to surface for air bubbles and also get oxygen from the water.

 

[hollyval]

Thank you for your suggestion. I just let the bag temperature adjust to the tank. I will try adding tank water next time. Yes, the 46g was very deep and they didn't swim all the way to the top to begin with. I recently set up a retangular 55g tank and moved my cories into it away from the loaches and also where oxygen is more accesible. They seem to be fine so far. I am keeping a close eye on them. I was just hoping it wasn't a ph issue because I can't adjust that successfully. I can change the other problems such as food and oxygen. Thank you again.
Hollyval