Panda cories dying

[Black_Rose]

Having a problem with my panda cories dying off.

Tank: 20 gallon tall
Tank has been running since Jan 1, 2017
Filters: eheim ecco pro 2234 canister, sponge filter.
Pea stone substrate with a small pot of crushed coral.
Two large Amazon swords, red root floaters, and floating guppy grass.
Gravel gets vacuumed once a month, 30-50% water change weekly.

These cories were all born and raised in this tank over the last few years.

A couple months ago, I started getting the occasional panda cory death.

I'd check ammonia, nitrite, and nitrate levels and all were good.

Since Sunday I've found 3 dead.

I checked the parameters last night:
0 ammonia
0 nitrite
<20 ppm nitrate
Kh 2 or 3
Gh ? (Test solution expired in May)
Ph 6.6 or 6.8 is what it looks like.
My other tanks usually test around 7.2

The older panda cories seem to be doing fine, but the younger ones are slowly dying off.
If I see one in trouble, it's usually laying on it's side.

I'm really at a loss as to what's going on, other than lower than expected ph levels (need to retest)

Any thoughts?

[lucodu]

Could your fish be suffering from poisoning of some kind?  Did you add a new element/decoration/substrate/plant with lead weight/etc. in the tank?

[Black_Rose]

There have been no changes to the decor, etc for well over a year, probably longer.

[Sherrill]

I've been having the same problem. I've lost two in the last few weeks. I've had mine for a few months. I lost three at the start when first introducing them, even after drip acclimation. I was disappointed but realize this can happen. Then everybody was doing well. No losses at all. All seemed happy. (I have eight left.)

I have a 65 gallon planted tank with a Seachem 75 HOB, a wave maker and my parameters are all at 0. pH is 7.0. I do a 25% water change once a week and use Prime. I dose daily with Excel (no CO2 injection) and twice a week I add the recommended dose of Flourish Comprehensive Supplement. This has been standard practice for me for months.

I've been wondering though. I keep my fish food in the freezer. My Pandas practically attack the Veggie Rounds that I feed -- in pieces -- every day or so. (I also have Red Cherry Shrimp and oodles of Red Ramshorn snails so I vary the type of food.) Could it be that they like the food so much they overeat and it swells inside them? I heard that can happen with Pandas.

[lucius]

I'm wondering if maybe the older Panda's are hogging all the food.  When you feed them, do you put it all in one spot?  I scatter all the sinking wafers and pellets around the tank so that there is less competition.  I also feed my bottom feeders about an hour after lights out.  All the faster tetras and gouramis are asleep so less chance of them going after the food.

Also do you notice if their barbels are short?  It's apparently a sign of bacterial infection. 

[Sherrill]

Thanks, Lucius.  I'll check those things out. I do spread out the pieces of wafer but I'll spread them farther next time. Also, picture me there with my magnifying glass counting barbels for the next several days.

[HayleYoyo]

I would look into one of two things:

Old Tank Syndrom

and

Corydora Toxins.

I have had no experience with either, but I've heard about them. Might be your issue.

[Sherrill]

Thanks for the replies.