Corydoras help in a new tank

[DwayneA]

A little over a month ago I started a new 29 gallon tank after being out of the hobby for about a decade. I cycled it and then over the course of a few weeks stocked it with 6 corydoras (3 albino, 3 green emerald), 4 plattys, 2 mollies, 8 danios, a nerite snail, and a betta. I was planning on starting the quarantine trio over the weekend anyway but on Thursday last week one of the albinos corys died. I went back to the store and got a replacement on Saturday did a water change and started the quarantine trio. Monday morning I checked on them and 1 molly and 1 emerald green cory was dead. Monday evening when I got home from work an albino cory was dead. And then this morning another albino cory was dead. Any ideas on what could be causing this? Other than the one that died they seemed healthy until I started medicating them. Now even the still living ones seem lethargic (could be do to no food?) and sometimes I'll see them laying on their side when I turn on the light. I did also have that one molly that died but otherwise the other fish all seem to be doing well. I thought it might just be from stress from the move and the medication, but I did have the one die even before I started the meds. I'm sure I'm missing something but I'm out of ideas. 

 

Water:

Temp: 79

PH: 8.0

Ammonia: 0

Nitrite: 0

Nitrate: 5

[DwayneA]

I didn't think to grab a picture this morning, but if it would help I can update with one after I get home from work tonight. And I don't have a hardness/alkalinity test for my aquarium yet, but I can tell you from testing it for my swimming pool we have about 150ppm Calcium hardness and about 200 ppm Alkalinity out of the tap.

Edited August 17, 2021 by DwayneA

[Colu]

I would do a 50% water change and add active carbon to remove the meds and add an extra air stone if you can get a picture that would help have they been eating ok no heavy breathing before they died it's possible something like  air freshener or other cleaning products could have got in to your tank  or they had a reaction to the meds 

[DwayneA]

Well I haven't been feeding them the last few days with the meds, but up until then they were. I have a HOB filter but I did add an air stone when I started the meds since I read they could make it more difficult to breathe. I hadn't even thought about cleaning products. The only thing I can think of is that I did use a dish cloth to wipe off the lid when I cleaned it. It was a clean cloth, but maybe there was some chemical on it even after going through the wash. Maybe I should try using paper towels instead? When I get home I can try changing the water and adding the cartridges back to my HOB since they have carbon.

[DwayneA]

 

Good news is that when I got home everyone was still alive. I changed the water and added the cartridges back to the filter and gave everyone a bit of food. I did note bubbles weren't popping as quickly at the surface. Almost like a bit of soap was in the water so maybe it was chemicals. I noticed it before but thought it was just due to the meds. Would it be a good idea to do another water change this weekend?

[Colu]

I would do another 50% water change and monitor for a couple of days if they are still not doing well I would do a course of kanaplex in they food just in case its a bacterial disease

 

[DwayneA]

Thanks for your help!

[TankofFish]

check your temp and PH also, both are on the high side  for cory's

Edited August 18, 2021 by TankofFish