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Discussion Starter · #1 ·
Hey guys,

I've been reading the forums for a while, but this is my first post. I recently had an issue I was hoping someone might be able to help me with. I just started EI dosing on my well established tank 2 nights ago, and yesterday I came home to 5 or 6 dead Tetras and the rest of my fish were all struggling at the top of the surface. I unplugged my C02, and did a nitrate test, and then a 50% WC. The nitrates were really high, somewhere around 40-80 ppm (they're usually less than 10; I tested my tap water, it's less than 5). Everything else in my API test kit was normal. The fish seemed to recover after that, but I have no idea what happened. When I did the first dose, I did 1/2 tsp KNO3 dry, 1/8 tsp KH2PO4 dry, and 1/8 tsp Seachem Flourish right after I did a 50% WC. I got the ferts from a reputable LFS that specializes in planted tanks. I also brought home 5 new tetras, put some new amazon swords in, and installed a pre-filter sponge at the same time. Here are my tank specifics:

45 gallon tall (36x12x24) - medium planted, medium stocked with fish
Finnex Fugeray Planted+ light 8 hrs/day
Ehiem canister filter
Pressurized CO2 with a regulator from GLA 8 hrs/day. I run it at 1-2 BPS, and it has been steady with no issues for about 4 or 5 months. Drop checker was a light green (maybe slightly lighter than normal), but nothing seemed to be out of the ordinary with it.

Any insight would be greatly appreciated! My first thought was that I had to have screwed up the KNO3 dose, but I double checked the doses with a couple different sources, so I'm really stumped.

Thanks guys!
 

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how long had the tetra been in the tank? Where they new additions? If so the co2 could be a reason for them breathing at the top of the tank, the water change removed the co2.

I have 2 tanks that run nitrates in the 60-80ppm range and the fish have been perfectly fine for 2 years.
 

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40-80ppm of nitrate won't kill your fish quickly, so that's not the problem. There's no established safe zone, but to do a rapid die-off mass-wipeout like that would require hundreds of ppm.

Struggling at the top suggests they were suffocating for some reason. CO2 would be my primary guess, but you checked your drop checker, so we'll pass on that for now.

Two possibilities that pop to mind:

1) you added new fish, which brings risk of disease. Check closely for signs of Ich and/or gill flukes (white spots like salt on fish, flashing, etc).

2) you added new fish, increasing bio-load. Did you test for ammonia/nitrite? Sometimes the biofilter takes a bit to catch up when the load increases, resulting in spikes. (which will likely be gone now, since the bio-load has dropped).
 

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Discussion Starter · #4 ·
The number of tetra died was the same of the number of new tetra I put in there, so I'm pretty sure it was all the new ones that died. I'm guessing whatever was going on plus the added stress of a new tank got to them.

I'm just not sure what could have happened with the CO2, it was still going at the same bps rate, and the drop checker seemed normal. My CO2 has been pretty steady for a while now. Would it make sense to lower CO2 for any reason when you start dosing fertilizer? Like the amount of CO2 that is good for an unfertilized tank is the not the same amount of CO2 that is good for a tank with regular EI dosing?
 

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Anytime I'm adding new fish to my co2 injected tank, I float them in the bag, and slowly add tank water. I don't add them to the tank until the co2 had shut off. That way the fish get 14 hrs or so in the tank to acclimate. I will also turn the co2 down a bit and increase it slowly over a few days back to where it was. You probably shocked the fish
 

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I checked for any ich, and didn't see any on the fish that died, and the rest of them seem fine. The new fish were cardinal and rummy nose tetras from 2 different tanks. I tested the ammonia/nitrites along with the nitrates. They were both close to zero.

Maybe I'll lower my CO2, and slowly step it back up, and do the same for the EI doses until I get a good balance (and definitely not add any more fish until then).

Thanks a lot for the input. I'll make sure I introduce any more fish slowly, and lower on the CO2.
 

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I checked for any ich, and didn't see any on the fish that died, and the rest of them seem fine. The new fish were cardinal and rummy nose tetras from 2 different tanks.
Oh, you were moving established fish between tanks? Or were these new fish from the fish store?

If you've had them for a month or more, I wouldn't worry about disease as much... from the store.. bigtime.
 
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