I have a 75g planted freshwater tank that's been set up for almost 6 months. Almost 3 weeks ago, I came home from the fish store with 8 new fish and some more live plants. I did a 25% water change to help place the plants, and then I introduced the new fish. I also cleaned the filters on my Aqueon backpack filter (I didn't clean my other Marineland backpack filter). I used API Tap water conditioner like I usually do. Within 5 days, I lost half of the new fish. Two weeks later, I had lost another one and did another 25% water change. As of today, I have lost 6 of the new fish, as well as 3 of my established fish. My tank is mainly composed of angels, tetras, giant danios, and gouramis. Apparently, you can't kill tetras as I've lost none since I set up the tank.
It appears the deaths were a result of the water change(s)? Am I correct in this assumption? The only steps I've taken to correct the situation (minus the water change) was to add API Quick Start this morning as I feared I may have killed too much beneficial bacteria.
Would need more info. Could be lots of things. Added 8 new fish? What kind? You mentioned some of what you already had but not the quantities. They survived a couple weeks.
First thing that comes to mind is bio media could not support additional fauna. Ammonia may have spiked.
But we need alot more info. Type fish and quantities. Filter, wc schedule, chems, ferts, plants, temp.
Before adding the new fish, I had about 5 angels, 8 tetras, 1 Dwarf Gourami, 4 giant danios, 2 small plecos, and 3 tiny catfish. I bought 3 black angels, 2 other angels (can't remember the type), 2 pearl gouramis, and 1 pleco. I tested my nitrite and nitrate readings, and they appear to be fine; however, I'm using strips, and I no they aren't as accurate. My liquid ammonia tester shows no traces of ammonia. I keep the tank's temp. at around 80F.
As far as filtration, I have a Marineland Penguin 350(GPH) backpack filter and Aqueon QuietFlow (400GPH) backpack filter. When I performed a water change last week, I remember rinsing the cartridges with tap water. Could this have killed all the good bacteria in the filter?
If those are common plecos there is way too many. One in itself is plenty for a 75g. Tiny catfish? What species? You have heavy waste making fish. Your over stocked.
Its recommended to rinse cartridges in used tank water from your pwc. I rinse mine but im on a spring fed well.
I always wash all my media with tap water when I clean the filter, so while that is a possible reason for why your fish died, it's not a foregone conclusion. But one thing is for sure - adding new fish is NOT the time for filter cleanings. Due to the timing of the deaths though, I do not expect that the cleaning has anything to do with it. Losing your cycle is a systemic problem that will affect your New and old fish just the same.
It's super important to quarantine new fish, for many reasons. Tops on the list is keeping diseases from being introduced to the tank and wiping out your stock. New fish have the highest mortality rate, so keeping them isolated from the main tank for a month or two is a great way to make sure only healthy fish are being added. You're spending all this time worrying about what you could have done, when it's entirely likely that the fish were doomed from the start.
I don't mean to keep throwing possibilities out there but that's all this is really. There are so many variables that it's rare there is a clear cut REASON why fish die. All we can do is make educated guesses. My best guess based on the info provided is that the new fish were not healthy. That theory does lend some credence to the possibility of the water quality being the issue, in that the stress could have been just enough to take out the weak fish (New and old), but not healthier ones.
So moving forward - no cleanings prior to adding new fish, no feeding for a few days after adding new fish, and quarantine new fish. The reason I said no feeding the fish is because new fish are often stressed and stressed fish can make other fish stress, and stressed fish don't eat. In addition to that, you just don't need to be making it any harder for the filter to catch up than it has to be.
No substrate is ok. Depending on stock you usually keep or want a 10g is a common quarantine. A 20 would be great. When ive had quarantine tanks I did prefer gravel though.
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