Pygmy Cory - Another Problem!

So sorry to hear about your cories, they are such sweet, easy going fish, either foraging or resting.  If it's any consolation you did all you could for them.

Anne

Thanks, Anne and Extreme_One.

There's no doubt that the transfer to the QT dramatically hastened the deterioration/demise of the final 3 fish, although I really didn't have an option as I was going to be going away for a few days' break and, with the cories not looking healthy at all, I didn't want to risk leaving them in the main tank with the others while away.  Whether this sudden deterioration was due to the stress of the move and/or to the eSHa 2000 or some other factor, what I would probably recommend to anyone who happens to read through this thread in future is to possibly err on the side of a smaller dosage of eSHa 2000 than recommended.  Having soft water, I could have doubled the dosage but didn't - with fish as small as pygmy cories, I would probably err on under-dosing, to be on the safe side.  [Dosage of meds is based on size of tank rather than size of fish but I do wonder if a micro-sized fish has more trouble tolerating the recommended doses.]

Based on my experiences, I'd probably recommend EITHER keeping pygmy (or pygmy-sized) cories with a similar sized shoal of micro-sized fish (eg CPDs or micro rasboras), ideally ones which swim in the upper echelons of a tank, OR in much larger groups if with small-sized fish (eg if with a shoal of 6 tetra-sized fish, then I'd probably keep 12 pygmy-sized cories to make them feel safer around their slightly bigger tankmates).

Now back to taking as best care I can of the x-ray tetras and harlequin rasboras who, oddly, seem to be looking much calmer/relaxed/'at home' in the tank than I've ever seen them, with a couple of them who had been repeatedly swimming up to investigate the cories' two corners on Sat evening already having claimed the cories' territory as their own...

Goodness - really sorry to hear about this. It seems as though once one goes, another follows, almost purely because of the previous one. I do hope that, in your case, this is a short-lived spell of bad luck and that the others will be absolutely fine. However, given my own experiences, I would definitely agree with the direction of your leaning - that's what, in hindsight, I wish I had done; I had been worried about overstocking but, reflecting back on the situation, I actually think slight overstocking might have been the better option for the fish - and, with pygmy cories, they wouldn't actually have had that big an impact in terms of ammonia produced, etc. If you do get more, then, if you can, I'd follow Diz1's advice to me which is to try getting them from another source/supplier.