Major die off after 40% water change + flourish excel double dose

[Nesopheus]

120gal low tech planted 2month old
PH 6.8
Ammonia 1 or less
Nitrite 1.2 mg/l
Nitrate 20 mg/l
GH 40
KH 40 mg/l

Dead

11 glass catfish, 4 pepper cory, 2 simensis flying fox
Survivors 3 gold gouramis, 4 dwarf gouramis, 2 powder blue gouramis, 1 pepper cory(last legs), 1 green cory, 4 kuhli loaches(some may be dead), 2 rope fish(1 confirmed), 1 large Plec, 2 oto cats.

I've kept fish for 20 years and I've never killed so many fish, uterly devastated. All levels read the same as usual except Nitrate and Nitrite. They were never so high. Doing a 30% water change now.
I appretiate any thing you might have to tell me, I will now curl up into a ball and cry.

 

[Ajno]

Maybe your water company added something to your water that killed off your fish. Thats the only thing that comes to my mind. I'm sorry for your losses.

 

[lipadj46]

the ammonia and nitrites suggest you are having a mini cycle, besides the excel (how much did you add?), anything else unusual happen?

 

[Nesopheus]

I use my own measuring tools so it wasn't the size of my cap (as read in other threads), 10ml/10gal
Water change, slight cloudiness next morning, strange ammonia/nitrate/nitrite spike. I kept 2 30gal low tech tanks without fish death for 3 years.

 

[Bderick67]

Are those water params before or after?

 

[cbugster]

What is the expiration day of flourish excel bottle?something went realy wrong with exel...cant think anything else...and the double dose??why??

 

[Nesopheus]

Are those water params before or after?

The test was done after the fact.
New bottle, no expiration that I can find.
Overdose for BBA, read soem threads about combating algea.

 

[cbugster]

The test was done after the fact.
New bottle, no expiration that I can find.
Overdose for BBA, read soem threads about combating algea.

anw....something went realy wrong with ur waterchange so take ur aquarium water to a chemistry lab. if something its in..maybe you gonna have more lost.

 

[shua71]

You're reading ammonia and nitrite after the water change. It was higher before the WC for who knows how long. Maybe the added stress of the WC killed them

 

[Nesopheus]

I have been testing bi-weekly. Can some one point me in the direction of an explanation for "cycling" I assume it has something to do with biofilter start up, never heard of mini-cycle.