So I got home from work yesterday.. and found my black/silver Tetra dead.. the other 3 tetra's are fine.. not sure what his cause of death is though.

Have you checked your water parameters? What are they? How long have the fish been in the tank? size tank? Is it cycled?

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How long did you have it, and where did you buy it? Some of the bigger chain stores get there stock from suppliers that don't have the highest quality fish.

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75 Gallon Planted

Yeah sorry I was a little General.. but heres more specifics.

Water Parameters: I did a water change two days ago.. liike a 40% change... added in seachem prime into tap water. nitrites are good, PH is good, it seems my nitrates are high.. and I can't get them to go lower.. (using API Test kit the water is a dark RED Color) I use a siphon to vacum the substrate.. and they eat all the food i give them..none of it really goes to the bottom.. unless I am doing the test wrong.. but the 3 other fish are fine.

Fish have been in the tank for a while.. at least a month or so?? two of the tetras have been in there since summer time

Tank Size: 10 gallon Tank

Cycled: Yes

This specific tetra used to always chase the other fish around (seemd to be very aggressive) My assumption is A. Nitrates killed him, or B. He was so stressed from chasing everyong around that he died..

Also I noticed on his Anal fin i guess? it seem to be either a little nipped at? or rotted.. but it wasnt red or anything like that.

all of my fish have been bought from Petco, I bought this black tetra and a white tetra same time.. and the white is fine.

It was just a thought. I know that I have bought some fish from Petco and Petsmart that have just croaked for seemingly no reason at all. I always check the water and what not after a death, but it has turned out fine every time. Maybe it was just his time. Never the less, it still sucks to lose any fish.

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75 Gallon Planted

Definitly because when I found him he wasnt floating at the top.. he was stuck on the filter (where the water is sucked in).. would that have killed him?

What is your normal water change schedule? Best time to test is just before your water change. That way you know how much to change. If you got a red color you are in the 80+ppm region. Enough to kill just about any fish if it is sustained. I would recommend weekly changes at least in the 30-40% region, if you're not already doing that. If you are, then you may want to to test your tap and see if you're getting help. I'd also recommend multiple changes to get below 40ppm.

Yeah I know this is not safe.. but idk if i'm just testing wrong or if it is actually this high cuz wouldnt my other fish be dying?? i have been changing like 35-40% of water weekly.. is this too much?

That could have been it. I have had fish stuck on filters before that have been just fine afterward, but I imagine every case is different.

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75 Gallon Planted

Yeah.. so i come down to the either he died from being stuck on filter.. or from nitrates being too high..

Not too much. Some fish tolerate high nitrates better than others. It doesn't mean that it can't/won't kill the rest if it remains that high. Test your tap and look over the instructions once more to make sure you are conducting the test exactly as it says - if you are unsure.

Yeah I may do another water change again today just to try and dilute it.. and test the nitrates on my tap and see what its like.

Usually when I have a fish die it ends up stuck to the filter. I think that's just the flow of the water..after death he doesn't swim and the filter sucks the water and he gets stuck to it.

So.. I did a water change and also vacumed some of the bottom to get some more crap out.. I tested my water for nitrates and theyres practically none.. however I changed the water.. added in some more Prime... and yet still nothing.. nitrates are still very high.. any thoughts?

If you did X% of water change then you should have seen X% change in your nitrate readings. For example...if you changed 50%, then nitrates should have been reduced by about 50%. If you didn't see any difference in your testing, then that sort of tells you how high they really are. Have you tested your tap for nitrates?

yeah i tested the tap water yesterday.. and the nitrates are very low in my tap.. I mean i saw a lighter red then it was before.. but it was still pretty red.. i put some of the prime in last night.. so ill test again today to see if that made a difference.. i dont wanna keep making water changes cuz i dont wanna like mess up the cycling ya know?

Water changes don't mess up cycles. There is very little bacteria in the water.

What kind of tests are you using. By the sounds of it, test strips and can be very inaccurate. Get a liquid test kit and it would be more precise.

You need to check not only nitrates, but also ammonia and nitrites. How long was the tank running before you added any fish? A healthy fish won't usually get caught on a filter, only sick, weak, dieing or dead fish.

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I am using the API master test kit.. the liquid one u pour i vials

Everything else is at stable and healthy levels.. only nitrates are high.. and my PH is a little high.. but the fish dont seem to mind it.. (cant give exact numbers at the moment)

The tanks been up and running for at least 5 months now? 2 of the tetras were first put in when it finally cycled.. and now these most recent two were put in probably at least a month or two ago... and the one died the other is still alive. Like i said the only signs of illnes were his anal fin was a little messed up.. he did jump out the bowl and fall on the floor for liek a minute when i first bought him.. not sure if that affects him at all either..