Cardinal tetras, platy, upside down then dead

Jasey

I have a 20 gallon tank that has been established for about a year now. I have live plants, elodea and Java Fern. The original inhabitants of my tank were 7 cardinal tetras, 1 Platy, 1 Paradise Fish, and 1 chain loach. Over the past 24 hours, all 7 of my cardinal tetras have died and just recently my Platy died.

Yesterday I noticed that a few of the tetras were swimming bizarrely, in circles, upside down. Then, they were just floating upside down although I could still see their gills moving. I did a 50% water change and used a double dose of Stress Coat. It seems after that then all of the tetras started exhibiting this behavior, and overnight they had all died. The Platy in the past couple of hours was swimming sideways, then went upside down on the bottom of the tank and passed.

The loach has been hiding in a cave, but when I lifted the cave to find it, it looks very pale with tattered/translucent fins. I'm afraid it may go soon too. The Paradise Fish is swimming regularly, but around its two side fins near the body it is very red, and looks as though it has a dark freckle near its head.

Here is what happened just before any of the fish showed any symptoms. The water temperature dropped down about 4 degrees F overnight (to 74 F) because I only had a 25 Watt heater. I bought a 100 Watt heater and put it inside the tank. The water temperature overnight arose back to around 78 F. That next day is when the tetras showed symptoms.

After I did the 50% water change, the water temp dropped down to 73 F, and with the heater it has since arose back to around 77 F.

I did a liquid test and the parameters are ammonia - 0, nitrite - 0, nitrate - 15, pH - 6.6

I just added activated carbon to the filter. It was previously running a sponge and BioMax insert.

Any help would be greatly appreciated so that I may save the lives of my two remaining fish, the Paradise Fish and loach. The loach is not looking like it will make it much longer. Thank you.

TwilightGuy

Wow, that's crazy, and disasterous. Sorry to hear it happened.

Did you treat the new water with Stress Coat before you put it in the tank or after? I think it's a clue that the Paradise Fish is the least affected, and it can breathe air. So, I'm thinking chlorine or chloramine poisoning perhaps. I don't think the temp change is enough to do that kind of damage. Or maybe the Stress Coat is old and lost it's effectiveness, if that's even possible?

I can't think of anything else at the moment, hopefully someone else will have something to add.

TwilightGuy

After re-reading your post, I have a question. Did the tetras you mentioned were swimming in circles and upside down start that behavior before or after you changed the water?

Jasey

Thanks for your reply. Two-three of the tetras had started swimming funny, circles, then floating upside down before the water change. Then they all started doing it after the water change.

I also added the double dose of Stress Coat after I finished refilling the tank with new tap water. The Stress Coat is not expired.

Byron

I too woulodn't have thought the temperature fluctuation described would cause this, but it seems it immediately preceeded it. Genetic issues can sometimes cause the described actions, but again one would not expect all the fish to suddenly develop this. Which means the cause, whatever it was, suddenly appeared in the water, either as a significant fluctuation in parameters or a toxic substance.

Nitrate at 15ppm with live plants like Elodea is perhaps indicative; and there is a sizeable fish load for a 20g. Prior to this, was tank maintenance regular? Water changes weekly, and how much? No substance aside from StressCoat entering the tank?

Did the tank pH remain around 6.6 prior to this? No sudden fluctuation, perhaps due to the tap water pH changing?

Byron.

Jasey

Thanks for your reply. The last water change before the 50% change was 1 1/2 weeks prior at 25% change. I make a 25% change every 1-2 weeks. I changed the sponge of the filter (AquaClear 20) every couple of months, the ceramic BioMax insert less frequently (~3 months). About a month ago I bought some liquid plant fertilizer (Aqueon Aquarium Plant Food) and dosed according to directions only twice in a week before I stopped using it. Unfortunately I purchased the test kit recently and do not have readings for pH before this happened.

I don't know of any substance that could have entered the tank in the time frame. The only thing I put in was the new heater. I did not rinse the heater before I put it in the tank. I am wondering if the heater is emitting a toxic substance. It is a TopFin 100 Watt heater.

Jasey

Very sad to say that the loach has now passed. The only remaining fish, Paradise Fish, remains the same. Still swimming regularly, but has much redness around its side fins where they attach to the body, and a small spot on its head. The water is slightly cloudy. I am considering doing a small water change (~20%) and adding the Stress Coat before I add the new water to the tank. I'm not sure if I should do another change when I just did a 50% yesterday but the water is a little bit cloudy today. I am hoping everything that the Paradise Fish will make it.

Byron

Provided tap water and tank water parameters are close (hardness and pH), daily water changes of up to 50% will do no harm. If it is something that was in the water this will keep diluting it. But beyond that, I don't know what I can suggest.

I would however recommend larger partial water changes once this is past. Weekly is minimum, the volume then depends upon the need. You had a fair number of fish for a 20g, and I would have suggested half the tank volume every week as the required change. Nitrates at 15ppm are not high, but higher than I wold expect in a natural planted tank. But there is much more we remove with a water change, "crud" that cannot be handled any other way. I change 50-60% of all my tanks every week. My tap water and tank water parameters are near-identical so this is not problematic. If they differ significantly, less water changed but more often works better, say 25% twice a week.

Byron.

Jasey

Thank you. The Paradise Fish is still alive, his status is the same. He is acting regularly, he ate some food, but the area where his side fins connect to his body is quite red and looks inflamed. I did a 20% water change last night and added Stress Coat to the new water before I put it in the tank.

Calmwaters

When you did the water change before the fish started acting strange did you replace the filter media? If so maybe it caused a spike in the ammonia/nitrite/nitrates which affected the fish?