Losing fish and don't know why...

[Mac]

Hi there!

I was invited to this forum from a conversation at Silverdale's Farmland Pets & Feed and need some help. My 90 gallon freshwater tank of community fish is losing fish on what is amounting to a day-by-day duration and I'm at a loss to what is happening. The community is made up of, or in some cases was made up of, 7 Cardinal Tetras, 6 Danios, 8 Rummynose, 2 Lemon Tetras, 3 Bosemani Rainbowfish, 5 Praecox Rainbowfish, 4 Rose Line Sharks, 2 Panda Corys and 3 Julii Cory Cats. I've lost all of my Lemon Tetras, 3 Cardinal Tetras, 2 Danios, 1 Rummynose, 1 Bosemani Rainbowish, 1 Praecox Rainbowfish, both Panda Corys and 1 Julii Cory Cat.

At first I thought it might be high nitrates as of two weeks ago it was almost 80ppm. This past weekend I went over to Dennys Pet World and purchased 20 gallons of reverse osmosis water to a water change and got it lowered to 20ppm. Still I'm losing fish. I've been told if water chemistry is causing issues rummynose lose color and the 7 that remain all look as colorful as the day I placed them in the tank. Currently chemistry is:
Ph - 7.4
Ammonia - 0
Nitrites - 0
Nitrates - 20ppm

None of the fish I've lost have had ANY symptoms of disease or problems with other fish. Today I came home to see one of the yellow danios now with a redness on oneside and losing color.

As the title says I don't why and could really use the help. Here are some pics of my soon to be lost Danio and my tank:
Danio

Tank 1

 

[Madness]

Any new fish added recently? What are you feeding? Have they been aggressively eating during this?

 

[Mac]

Thanks Madness!

Yes, I did add the Rainbowfish about a month ago however there hasn't been any aggression between them or the original community nor during feeding. Haven't changed their feeding either, I still use a mixture of frozen bloodworms and flake food.

Another fish lost - Cardinal Tetra...

 

[Madness]

During this, how often are you doing water changes

 

[Mac]

I do 10 to 20% water changes weekly. Since this started I've been doing 10% water changes.

About to lose a Rainbow...

 

[Madness]

You should be doing at minimum 50% weekly, and more like 10-20% per day while this is happening

 

[Bob]

I know you are not quarantining fish, but this will give you lots of info on the medicines out there, and some you may want to try.

https://www.youtube.com/playlist?list=PLNM4mDAXGxWy_XtG7TtBsRXmErhPpJrie

 

[Mac]

Madness - Thank you! I'm going to do a 50% water change at my earliest opportunity. Hopefully it will curtail the loss of fish soon.

Bob - Thank you! The links definitely gave me a new insight on getting new fish and ensuring anything they might bring with them doesn't infect the rest of the community. Gained a LOT of knowledge I never even considered. Now to convince my better half on getting a small quarantine tank....

 

[Mac]

Update: I've lost a couple of fish since this post a week ago. Performed a 50% water change yesterday as well as added E.M. Erythromycin and API General Cure to see what I might be able to save. The Erythromycin provides a yellow tinge to the water but if it stops the kill-off I will be ecstatic... Will keep the forum up to date.

 

[Mac]

Update #2: After a total of two 50% water changes and multiple medication adds, I'm down to 4 Rose Line sharks, 5 Rummynose, 3 Cardinal Tetras, 1 Danio, 4 Praecox Ranbowfish and 2 Julii Corys. I've lost a total of 21 fish from when I believe this started AND it has been almost a week since I have lost a fish so my fingers are crossed the tank & community is on the rebound. This has been a real lesson for me on introducing new fish to a community.

Thanks to Madness & Bob for the greatly appreciated insight and assistance!