Sterbai Corydora Bloating

Hi all, I'm back again with another question, I had 4 Sterbia corys in my large community tank, after doing some renovations to my tank, due to it having black beard algae, my water readings peaked for a while but everything has been running as it should, we then noticed that one of the four Sterbia corys looked bloated and it's general colour was very pale, it died a couple of days later, I have tried to google the problem, but I don't really seem to get much in the way of info back.
2 of the remaining 3 then became bloated, and their colour looked pale so I decided to try treating with a general tonic that is effective against mites, fin rot and white spot, it did not seem to have any effect at first, but in the past couple of days the bloating seems to have subsided and their colour is looking much better, while I'm happy that they are looking better if anyone has any ideas as to what the problem may have been I would very much appreciate any info that anyone may have.
Thanks

Hi Matt, they get a mixture of algae wafers, hikari micro granules and frozen (defrosted obviously) blood worm, brine shrimp ect

Ok thanks for your input anyway Matt will leave this up to see if anyone can help

I'm sorry that I don't think I can be of much help other than to empathise.

I had pygmy cories, all of which died between months 6-9 in my tank, of similar problems to what you describe but additionally other problems (including partially-/fully-severed tails, pus-like lumps and bloodstreaks under their pelvic/anal fins), despite water parameters being in line with their requirements, water quality being consistently 0 for ammonia and nitrite, and 20 for nitrates and despite a varied diet. All other inhabitants were fine - initially x-ray tetras, then also harlequin rasboras. Having exhausted all obvious options, I've put mine down to either:
*the tank being insufficiently mature when I got them (not long finished cycling although it didn't pose a problem during the first 6 months of them in the tank);
*being harassed or feeling intimidated by larger tankmates (in particular two female tetras who lurked around them, waiting for food debris being foraged, although there was no sign of them being perturbed and they were quite happy foraging in dispersed locations around the tank rather than in groups or hiding);
*6 (but dwindling in numbers) being an insufficient number .v. the size of their tankmates

Might any of these be a possibility? [Here are a couple of useful profiles for the sterbai cory - perhaps an additional few might help? Are your water parameters suitable for them? http://www.thinkfish.co.uk/fish/sterbai-cory.html and http://www.seriouslyfish.com/species/corydoras-sterbai/]

Mine didn't respond well to the eSHa 2000, and, in retrospect, I wished I'd dosed lower than suggested, particularly as they were so tiny. On that basis, although yours are bigger in stature, I'd err on the side of underdosing any medication you try.

Best of luck, and sorry I can't be of any more help.