Dying fish - help please!

[shobxrs]

I have a well established 55 gal community tank. I recently added 6 ottos to the tank. I did not quarantine ( I know, I know!!). Well several days after I started losing tetras suddenly. Now I've lost an angel, a Cory, a Bosemani and a few more tetras. The initial fish i lost did not seem to have any physical issues. The recent loss, Bosemani, seemed to have color loss and some possible grey patch and a few red places. Not seeing white spots,like Ich. I did a huge water change when I started losing fish. Yesterday I started adding Maracyn and Tetra Life Guard. I totally do not know what I'm dealing with. Help!!

[mommy1]

If you don't know what you are dealing with then don't medicate. It's possible your new fish brought some sort of internal parasite with them and neither of those medications will do anything. Do the otos or any of your fish show any sign of parasite, sunken or swollen bellies, red gills, red patches on their skin, etc?

[shobxrs]

None of those signs except on the last fish I lost there seemed to be gray area on the skin. That is what has me so stumped, no apparent signs that I can see or detect.

[shobxrs]

Also, there were a few red places in the gray area.

[mommy1]

What are your water parameters, ammonia, nitrite, and nitrate?

[madagascariensis]

it is likely not an internal parasite, as these tend to progress slowly, with visible emaciation and other symptoms weeks before death.
I would guess an external parasite, something like velvet.

[shobxrs]

I have checked my water params and all checked out. Ammonia at 0, nitrites at 0. I also did a big water change, 80%, when I started seeing the sudden deaths.

[madagascariensis]

did you possibly forget to dechlorinate the water? how about temperature matching?

[Cermet]

An 80% water change can cause a huge pH change if you have soft water. Do you know the pH of the water in the tank and that of the source water? Remember, a pH change over 0.25 can kill fish! I assume that the original deaths all occurred after the WC? If so, this could be the issue assuming Madagascariensis' point isn't the cause.

Also, what are the nitrates (before the WC?)

[shobxrs]

The WC was after the first 5 fish died suddenly. I checked my water params prior to the WC to make sure I didn't have anything going on. Yesterday I took the last dead fish to a LFS, not where I got the Ottos. This guy has had the store for 25 years. He said it didn't look or sound like external parasite. He told me to double my dose of Maracyn first day, then continue with Maracyn as directed. I did and I haven't had any losses over night. I'm hoping the Maracyn does the trick for whatever this is.