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Tank Turned Deadly Overnight


Skimmy

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I'm in college, and my mom takes basic care of my fish while I'm away and I come back about once every 3 weeks to a month to do 50% water changes in my 10 and 20 gallon tanks. This has been working out for the last year and the one fish in each tank has remained healthy and all levels have been steady and safe. When I came home yesterday and checked the tanks, they had considerably more green algae than usual, mostly due, I think, to my mom leaving the aquarium lights on too long. So here's the story of what happened.

The 20 gallon had considerable algae on the bottom, and being as the substrate had been there the whole time the tank had been set up, I decided to change it. At this point the telescope goldfish in the tank was behaving totally normal. I put new pebbles down, did a 50% change, cleaned all the green algae off the tank walls and filter, changed the padding and carbon in the filter, and tested the levels (0 N2, 0 N3, 0 Ammonia, 7.8 pH - the same as it's been for the last 8 months). When I woke up in the morning, the goldfish was laying on an angle at the bottom of the tank and appeared to be gasping for oxygen. I left to pick up some salt and a new air stone, got back, and after two and a half years of good health, poor Brutis was dead. I chalked it up to simply the fish being old and getting shocked by the sudden change. Now the second part.

The 10 gallon tank had gotten new substrate somewhat recently. The black moor I keep in there has also been extremely healthy the whole time I've had it, despite it getting swapped often from tank to tank due it being a little violent. After the salt had filtered a bit and the air stone had been running a few hours, I swapped him into the bigger tank. His small tank had the same levels, same temperature (70 degrees F - forgot to mention that), filled with the same tap, and also had relatively new stones on the bottom, so I figured it wouldn't be that big of a change. Well I put him into the big tank, he was fine for a minute or two, then he too sank to the bottom and began gasping for air same as the other did. The fish that died had bottom sat a few times in the past, but this was literally the first time in two and a half years that the black moor ever stopped swimming and appeared weak. When I quickly moved him back to his smaller tank he immediately perked back up.

So my question is what could have possibly happened in my tank that suddenly caused my fish to suffocate in it? Something obviously must've gone drastically wrong, but I can't imagine what it was. The only thing that was altered was the pebbles on the bottom. Could something about them have caused this? Thanks in advance and sorry for the long post.

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Hismile.gifSorry you lost your fishy friendundecided.gif In changing and cleaning everything at once in your larger tank,the tank's equilibrium was thrown completely offundecided.gif Substrate(gravel) should be changed out very slowly-over a period of weeks,b/c beneficial bacteria live there,and also,when you disturb that much gravel-especially every 3-4 weeks-it releases too much nitrifying bacteria at 1 time. Also,you should never change more than 1/3 of your filter material at 1 time-the beneficial bacteria that perform the nitrogen cycle live there. It sounds like you probably did too much,and lost your cycle,and stirred up too much of the bad bacteria. Also,do you do a temp. and Ph matched water change? Did you do a nitrate test? What kind of test kit do you use? This is all important information.

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I agree with kukana. I just read online about toxic air pockets in gravel that can build up if the gravel isn't being stirred around on a regular basis. And if the gravel is stirred after a longer time those toxins can kill your fish, it seems to me that this is the case.

From now on, try to get your mom to do a partial water change at least every other week, better even weekly. Even if she changes only 20% by doing some gravel vacuuming, this will make the conditions for the fish a lot better and will prevent toxic air pockets from forming.

Sorry for your loss though :(

Also, since you already are "short" one fish now: Even fancy goldfish should not be kept in tanks smaller than 20 gallons. I would move the moor into the 20 gallon tank and keep him there for good. But first do a good, thorough cleaning and disinfecting of that tank, then move the filter media of the small tank (which wasn't affected) into the big filter.

This will keep the moor healthier on the long run :)

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I guess the gravel thing does make the most sense since that was the only thing I did different than usual. I did do a temp and pH matched change. The kit I use is from Aquarium Pharmaceuticals. About the filter media, I use a Penguin filter and usually change the padding and carbon (only two things I use) at once because I was under the impression that the bio-wheel is enough to regulate the cycle. The black moor will be switched over, his 10 gallon does get way too filthy way too fast, it's always just been a matter of space and the fact that he always attacked the one that just died so they had to be kept separate. Thanks for the quick responses, I'm glad I at least know what I did wrong so that I never do it again.

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You're welcome! Apparently your black moor is a loner and doesn't like company, so it won't hurt him to be in this tank by himself. He will actually turn out to be very happy and quite healthy. And as you said, a lot cleaner. As you probably know, in a properly stocked goldfish tank you need to change about 50% of the water weekly. I understand that your mom might not want to get into all this, but if she can do at least half of that (like every other week 50%) it will be much better for the fish.

Additionally you could try to use the filter of the 20 gallon and the 10 gallon tanks together in the tank, which will raise the filtration by at least 50%. And as said, the less gravel/rocks on the bottom, the less waste will remain in the actual tank, especially if you manage to extend the filter intakes to the bottom of the tank. I did that with black flexible tubing, it is not the prettiest thing in the world but works AMAZING. Sucks all the poop right off the bottom of the tank and that way you will never have to worry about air pockets in the gravel again :)

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