It's just embarrassing. It was really the perfect storm of everything you've ever learned through fishkeeping school that you are not supposed to do. So, if people avoid doing everything this fine forum advises against, they should be good 🙂
I have a mature 75 g tank with a whole host of fish and plant life that hasn't had any new fish added in over 6 mos (maybe even closer to 9 mos). No additions, no subtractions - just bliss. I wouldn't say that it was overstocked, but it was well stocked.
Diamond tetras have been on my list for about a year, and last week I went on a road trip to my favorite fish store just to check things out. They had the most beautiful, fat and healthy diamonds I've seen yet and couldn't resist picking up 6. I also wanted to add to my otocinclus clan, as I only had 4. I picked up 3 more on my trip.
Lesson 1 = QUARANTINE. I did not. They were so healthy looking (as is every single thing I buy from this store) that I tossed them right in. Two days passed and life was good.
On day 3, I had a dead new otto. I was a little surprised, but chalked it up to a stress death or something like that. The next day, I had a random neon tetra death. Ok, that caused me pause. I checked water parameters with strips and also the kit as a back up. Parameters were perfectly normal. The next day, I lost a black neon and another neon. Still normal water parameters. The next day, lost a borneo sucker, another black neon and another neon. Still perfect parameters - 0 ammonia, 0 nitrites, ~20 nitrates. Water was clear. I'm thinking, if the water is fine, there's no need to change it. I had just done a water change the day before adding the new fish. I didn't attribute this to bioload, I attributed it to sick fish.
So, I figured, it's been a solid 9 mos or so since the tank had been treated and with these new fish, better to be safe then sorry (I was already feeling pretty sorry). I decided to treat the entire display tank with the med trio and did so last night. (Maybe lesson two should have been to remove the new fish and put them in quarantine instead of treating the whole tank!)
I didn't go back to check on them this morning because I've done this before without incident - it's how I treat all new fish in my other tanks.
Lesson 2 = MONITOR MEDS. If you use them ... keep an eye on things.
Today, when the lights popped on shortly after noon, my husband called to me that the tank looked cloudy. Meh, no big deal. That's to be expected when you medicate.
I took my time getting over there to see what was up. I bent down to look. It wasn't the cloudiness of the water that concerned me. What concerned me were several dead tetras belly up and all of the rest of fish (INCLUDING MY PLECO) at the surface of the water gasping for air.
I stuck my hand in the water and it felt HOT. Checked the temp and it hadn't changed. I assumed that the heater was burning out on me and frying my fish and that my thermometer was broken. That's when I added another airline/pump and removed the lids.
Ha! I have literally no idea why that was my next action.
Lesson 3 = CHECK PARAMETERS FIRST! When you see cloudy water, check your parameters and do a water change!
10 mins goes by with no change in behavior.
In my panic, I hastily grabbed all of my equipment and did a 25% water change and replaced with cooler water (smacking my forehead right now).
Puzzled, I left, asking my husband the check parameters for me. He said, "That can't be the problem. We just checked them last night and they were fine." I encouraged him to do it anyway.
NITRITES were higher than we have ever seen in our lives! I didn't even know these kinds of results existed!!!!
And the bloom! It must be bacteria!!
I immediately did a 50% water change.
Things are better. Nitrites are there, but barely.
I will now spend the next many - many - days recycling my tank with all of my display fish in cycle with multiple water changes a day. It's not ideal, but with more fish on the way tomorrow that I purchased online over the weekend - I don't have a choice. Those new fish are going straight into my cycled quarantine tank and my other tanks are full.
So that's my story.
It's all wrong.
Every bit of it.