Hello Team Aquarium Co-op, few weeks ago i bought around 10 pygmy corydoras added to my existing 20 gallon tank which already consisted of around 40 endler/guppies and few panda cory and few other corydoras. After few weeks i saw which I thought was ich on one of the guppies. So i attributed that to the pygmy corydoras as i went to online and found that adding new fish can cause ich. I was sure coz I did not had this issue before so i added salt and increased the temp and it seems to improve the ich on the infected guppies after few days. So yesterday I bought an ich x and added (10ml) using oral syringe to the 20 gallon tank and forgot to water change so when i woke up today in the morning i saw 1 dead stripe corydoras not to forget virtually all my pygmy were dead and panda corydoras were on verge of death like they were very lethargic and barely moving. So i did a 40% water change today (added stress coat which on hindsight probably wasnt a good idea?) and did not add any medicine (Ich-x).Can anyone help me what went wrong here and what can I do next, one being the obvious not doing the water change before adding the ich-x and I am still wondering how it effected only my corydoras and not the Endler/Guppies?As you can see in the pictures some of my panda corydoras are still acting very weird like sticking towards filter sponge and some hanging upside on the floating plants as you can see in the picture but my endler/guppies are all fine.Any kind of feedback would be helpful