Mysterious illness killing fish in under 24hrs

[Alexp08]

Hello, so I have this mysterious illness that is taking my fish in a very quick timeframe. I started about 3 weeks ago on which I lost about half my stock in my 150gal community tank. I started treating with metroplex and sulfaplex, didnt see any response, then I went to ammoxicilin and paragaurd, and really didn't see any results. So I tried all 4 at the same time. Well the dying stopped and I went a week with no fish deaths. Well it's happening again. It manifests as cotton mouth, a lose of color/fungal? Around the tail area, or a dorsal fin event. I've been trying to remove infected fish and place them in a hospital tank, but really that prove no benefit as by the time they show symptoms, they are literally gone within 24 hours, it's attacking all fish, I've lost 2 plecos today, one Cory cat, and a Odessa bard. Yesterday was a neon Tetra.

I have attached pictures.
On hand I have
Metroplex
Sulfaplex
Amoxicillin
Paragaurd
NLS hex gaurd
Prazipro

Any help would be appreciated. Thanks

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[NickAu]

Hi

Tell us more about this tank.

Is it filtered
Has it got a heater
What is the water temp.
How big is it
Is it cycled
How often do you change water
How much do you change
What water conditioner do you use

The more info you give us the better.

 

[Alexp08]

It is a 150gallon heavily planted tank, temp is set to stay at 78F, 30gallon sump, been up and running for about 6month now. Water changes every week, about 30% water change, I use prime as a water conditioner.
Ammonia 0
Nitrite 0
Nitrate 10ppm

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