Hellow all, I am really bummed out to have lost all my Striadas this week, two which I have had for almost 12 years and been with me through a few heartbreaks and GFs. A week ago I added a couple new materials to my river tank, a large piece of green dense foam and a soft plastic mesh. One or both of these I believe to have contaminated the water. I lost all three Striadas and one recently aquired Schistura (seen on a photo I posted)
The odd thing is not all the fish were affected the same way or were as sensetive to the contaminant. Only two clown loaches and the Kubotia seemed to be doing well throughout and was not affected. All my other clowns, my tigers and my one and only beauforti seem to be acting as if they are crippled by wobbleig their whole bodies while they move/swim. Their stomachs also got concaved in a short period. Really unpeasant sight in my tank.
A couple days after I installed the materials, even before the lights were on, I thought it was unusal to only see two or three fish plus dither fish eating when I feed them. I made nothing nothing of it as I left for work. After three and four days the striadas died one by one. I thought it was odd but they been friends for a long time and I thought it was greif and old age. With the few plump healthy loach and the occasional head of the others peeping out of the caves, it did not occur to me that the water was bad. A couple more days of not seeing the loaches completely come out made it hard for me to ignore the feeling that something was really wrong.
I did an inspection in their labyrinth of caves and I had to coax them out only to be shocked and heart broken by their condition. I immediately did a 90% WC and during it they came out of their caves all wobbly (possibly to be in the fresh water). It has been two days since the WC and they are still wobbly but most are eating and out and about, atleast when the main lights are off. The clown that has been affected the worst has not eaten yet, atleast not that I have seen but she seems to be doing better because she came out and got the strength to be a little grumpy to reclaim her cave from an intruder. I do hope they get better.
I take it you've removed the suspect items from the tank now? I would keep up the water changes and insert a Polyfilter (which absorbs all sorts of nasties) into the filter. Not sure how commonly available they are over in the US, here is a link to one site which shows you what to look for: 
Keep us updated!
