Thanks,for the info regarding David Sands. I too did some googling after your mention of Mr. Sands.
I find this to be a perplexing problem. Is suggested that lifespan of Jullii corydoras is 3 to 5 years,Perhaps they are approachig senior citizen status like myself.
I find it quite odd that Kuhlii loaches and YoYo loaches seem unaffected, but then they aren't kept in the same tank but over same substrate in other tanks.
Some suggest that a lack of current flow along or near the bottom is,or could be,, contributing factor..
Yesterday, I lowered the temp to 74 degrees from 77 degrees F and performed a 50 percent water change although my nitrAtes tested at 10 ppm. I also placed a powerhead at the bottom of the 56 gal tank that is filtered with an Emperor 280 and a Hydro V sponge filter. I am going to change 50 percent of the water twice a week for a while and vaccum one half the substrate (fine gravel) at each change, and observe for a while. Funny thing ,,after the water change, Corys began spawning activity. They eat as always ,and remain active but I am just as likely to wake up to a dead cory if symptoms hold true to form.
I also have seen this anomally? with other species of corydoras over the years but until now,, I have simply replaced the fish when they expired.
I am going to purchase another group of the julii if I can and perhaps use them as control group in as close to same enviornment as I can except for current along the bottom (not a scientist) ,,And study all of them. Perhaps I will stumble upon a common denominator (or not) ,,that will help me to understand possible contributers.
Have nixed the idea of reverse flow UG filtration for I really don't want to take down the 75 gal that holds as of this moment ,approx 40 baby long finned albino Bristlenose,long finned Blue Danios,and glowlight tetras. This is also the tank i wish to once again set up with plants come spring.
For now,, I shall try the twice or three weekly water changes , along with the additional current along the bottom and gravel vaccuming and see what benefits are realized. Those I have corresponded with thus far ,are of a mind that the fishes can and do carry on quite well in clean enviornment,with or without barbels but it troubles me just the same. Catfish just look funny without their barbels,kinda like a tall skinny guy like myself ,in shorts.