Strange Things Happening In My Tank

HI All,

New to the forum but have been reading it for years.

Yesterday I upgraded my 15 gallon (60L) to 50 gallon (200L) using all the established gravel, filter media etc from 15 gallon that has been running for the past 3 yrs. Fish in tank
1 molly
1 balloon molly
1 DG
2 upside down catfish
1 common pleco (love this guy!)
4 zebra danios (added today)

Tested water this morning and all good
Nitrite 0
Ammonia 0
Nitrate 40
PH 7.2-7.4

Then today I noticed that two of my fishies have a strange blackish layer on them. The molly's fin also seems to have a black edge and the DG seems to have this blackish stuff around his mouth area. Both feeding well.

Added 4 zebra danios this afternoon (before I noticed the black stuff, otherwise wouldn't have done so) and things went downhill from there. First I noticed the black stuff, then I noticed that 2 of the danios have eyes missing. Placed them in qt tank for observation but they seem to be doing fine.
This evening I noticed that my molly (very pregnant at the mo) keeps dissappearing and hiding around the tank. Now I wouldn't think too much of it under normal circumstances since she is about to drop the fry pretty soon, but my balloon molly and the DG are doing the same thing and seem to krep to the bottom of the tank.

Are they sick and if so, what could it be and how do I treat it? Have had my aquariums for three yrs but haven't had to deal with a lot of diseases to date so no idea what to do

PS: pics attached are not great, I know, couldn't get them to stay still

 

>inb4 pleco needs 200,000 gallon tank
move common pleco. you have poopoo getting on their skin

 

I can't see any black stuff.
Did you use a new carbon filter without rinsing it first?

 

Welcome to fishlore!

>inb4 pleco needs 200,000 gallon tank
move common pleco. you have poopoo getting on their skin

Well common plecos need over 180 gallons

 

I can't see any black stuff.
Did you use a new carbon filter without rinsing it first?

No, always rinse carbon pretty well before use. I know the pics are really bad, will try to take some better ones in the morning. Currently more concerned that they are all hiding and lingering at the bottom. Convinced molly tried scraping against the rocks just now, but don't see anything that could even closely resemble itch

 

Welcome to the forum anyway

Any change the new tank came in contact with soap or any other contaminant? It is odd that fish are suffering. I would make frequent water changes.

 

Thanks Piaeliott
Definitely no soap or contaminates that were even close to my tank. Mollies are much better this morning, swimming around like usual. DG very lethargic and keeps heading for the bottom corners, just lingering there. Moving it to qt tank for observation today. Water parameters still all good this morning