Slowly losing fish

[Mebbid]

For some reason I have been slowly losing fish over the past few days in my heavily planted 55g community. So far the count is up to 1GBR 2 Australe Killifish and 1 Guppy. I recently had a columnaris infection that I treated for and there no longer seems to be any visible signs of infection. Along with that I also treated with a round of Metronidazole medicated food which was gleefully eaten.

Levels:
Ammonia: 0
Nitrite: 0
Nitrate: 5ppm

Water changes: Weekly 40%
Days since last water change: 6

I was wondering if wildly fluctuating nitrate levels could be causing issues since that is part of my fertilizing schedule.

The only other thing that I have changed was an increased amount of fertilizers about 3 weeks ago.

Stocking List:
1GBR
3 Fancy Swordtails
8 Harlequin Rasboras
4 Panda Corys
8 Guppies
2 Bristlenose Pleco
1 Orinoco Angel Pleco
20+ assorted fry
30+ shrimp
Lots and lots of snails
Assassins, Pond, and MTS

The only aggression I've ever seen was between the two bristlenose plecos but the tank is big enough that only really happens during feeding time

 

[Convict2161]

For some reason I have been slowly losing fish over the past few days in my heavily planted 55g community. So far the count is up to 1GBR 2 Australe Killifish and 1 Guppy. I recently had a columnaris infection that I treated for and there no longer seems to be any visible signs of infection. Along with that I also treated with a round of Metronidazole medicated food which was gleefully eaten.

Levels:
Ammonia: 0
Nitrite: 0
Nitrate: 5ppm

Water changes: Weekly 40%
Days since last water change: 6

I was wondering if wildly fluctuating nitrate levels could be causing issues since that is part of my fertilizing schedule.

The only other thing that I have changed was an increased amount of fertilizers about 3 weeks ago.

Stocking List:
1GBR
3 Fancy Swordtails
8 Harlequin Rasboras
4 Panda Corys
8 Guppies
2 Bristlenose Pleco
1 Orinoco Angel Pleco
20+ assorted fry
30+ shrimp
Lots and lots of snails
Assassins, Pond, and MTS

The only aggression I've ever seen was between the two bristlenose plecos but the tank is big enough that only really happens during feeding time

My guess would be the columnaris. That's a nasty one and one that killed 20+ fish in my 75 gallon. Just cause they weren't "showing" doesn't mean they weren't infected.