Persistent Ammonia and fish dying

rrkss and star_rider, thank you guys for your help. I did the 90% water change and added Bio-safe and the Bio-Spira. I also got a bottle of Prime. You weren't kidding though, it is concentrated. For a 12 gallon tank, I only need about 1.2 ml for a full water change so a 20% water change would only be around 2 to 3 gallons, so I would only need to add 300 microliters of Prime and unfortunately not many measuring devices go that low. Guess i'm going to have to do some serial dilutions...

Hopefully my remaining fish will pull through. And i'll definitely think about a quarantine tank though i have no idea where i would put it. I live in a tiny dorm in new york city and space is pretty precious.

I do have another question though. When i was pouring in the new water, a lot of clumps of bacteria started floating around in the tank. It was a greyish color and since my tank didn't seem to be cycling at all, I went ahead and tried to remove the big chunks of bacteria. You guys have any idea what that kind of bacteria is? Is it the good kind or bad kind? According to a marineland article, the ammonia bacteria are reddish orange, and the nitrite ones are tan, and mine where neither. My other question pertains to neon tetra behavior. I have this one neon tetra who is hiding in this tall cave decoration with his tail toward the sky and head towards the gravel. Anyone have that sort of behavior before from a tetra?
 
Haha, why didn't i think of that... that shouldn't be so hard to get since i'm a med student. Thanks for the tip!
 
rrkss, the advice you gave is great!

So, yesterday, did 90% water change with Bio-safe and added Bio-spira
Today:
Ammonia: ~0.05 (It is just a tinge greener than my control but definitely no where near 0.25)
Nitrites: 0
Nitrates: 4 ppm
pH: went from 7 to 6.9 or 6.8, which i guess is a by product of the nitrite bacteria... do i need to do something to increase some sort of buffer in my water so the pH stays more constant in the future?
 
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