[Zoidborg]

Not sure what this white stuff on my peppered corycat is. I added three new peppered cats to join my existing pair that's over a month old. One day later my oldest and largest cat has this growth on its dorsal.

First day pic

To be safe I started adding daily 10 mL of Seachem Paraguard to my 20 g to treat the whole tank. I lost one corycat (one of the newbies) to an unknown issue, it had no white spots on the second day.

Now a total of 4 days later, the growth on the oldest corycat is half the size and no longer as fuzzy as the first day. The rest of the tank is doing well, showing vibrant colours and no stress.

4th day pic

What is this growth? Did I treat the tank correctly?

 

[The Trigger]

Could be a fungal infection. White fuzzy stuff is a dead givaway. I've found keeping the water super clean is the best way to prevent fungal infections. I'd do a large water change in combination with an anti fungal medication

 

[Zoidborg]

Thanks the trigger for the info. Forgot to mention on the second day, I did do a 50% water change. Normally I do 25% weekly, my readings are always 6.8 ph 0 ammonia, 0 nitrite, and vary between 5-20 nitrate. My tank has live plants aswell.

 

[The Trigger]

Judging by the second pic it looks like it's clearing up so I'm guessing you're doing it right. Probably had a cut or scrape that got a fungal infection. Just keep observing them and make sure the water quality stays high. Usually clears up on its own.