My 30 gallon aquarium has been up and running for 9+ months and it has been more than 6 months since I last had a problem in this tank (there was an ich outbreak early on, shortly after adding a new fish.) Tank inhabitants are as follows:
5 brilliant rasboras
3 zebra dianios
3 platys (1 m, 2 f)
3 cardinal tetras
1 java fern (and lots of plastic plants) -- the fern has only been in the tank about 3 weeks; it's my first attempt at live plants
These fish have been thriving, with the exception of the ich outbreak, for 9 months. I stocked the tank slowly, perform weekly water changes, change the filter media every 3 weeks, and monitor the water quality. I did my weekly 25% water change on Monday evening, adding AquaSafe and Alage Fix as usual. I didn't notice anything unusual about the fish behavior at that time, nor had I in the days before.
On Tuesday afternoon, I found a rasbora swimming upside down. By Tuesday evening (24 hours after H20 change), 2 rasboras and a zebra danio had died. I checked the water quality, and everything looked OK -- ammonia and nitrite are reading at 0, and nitrate is at about 20 ppm (not perfect, but it shouldn't be lethal, and yes these are the chemical kits, not the test strips.). I did another 25% water change and later noticed that more of the rasboras were swimming erratically -- almost as if they were drunk. By Wednesday evening (so, 48 hours after the first H20 change, 24 hours after 2nd H20 change) I had lost 4 rasboras and all 3 zebra danois. This morning (Thursday), one of the platys was dead. This afternoon, another died.
I have noticed that the dead bodies appear a bit bloated, and there are dark spots on the bellies -- internal bleeding, maybe? My platys also clamped their fins, something the others did not do. One platy also looked very skinny -- I feel like this appearance came on very rapidly, but maybe I've just missed it somehow?
Only the cardinal tetras seem 100% oblivious to whatever is going on in the tank; they are still swimming around and eating like normal. The remaining platy still looks perfectly healthy as well, but the last rasbora looks like he might be getting sick -- I can't tell for sure.
Any ideas? I'm stumped. The only thing I can think of is that perhaps there was a problem with the city water. I haven't done my regular water changes on my other 3 tanks because I'm afraid that's the problem. It just seems so sudden... I have accepted the fact that I will probably lose all the fish. What I want to know is, what went wrong? What should I have done differently? And how can I avoid repeating this problem once I re-stock the tank?
If this is not a water supply problem, what would cause it? Like I said, I am very good about water changes, monitoring water quality, adding water conditioner, and changing filter media, so...?Fish Suddenly Dying -- Help?!?Two things come to mind. Temperature and disease. Fish can stress out if the water added to the tank is drastically different (either too hot or too cold). I imagine this isn't the case as you do a weekly change, but it has to be ruled out. Rasboras can be sensitive, but what is strange is that the cardinals seem unaffected b/c they are as sensitive, if not more sensitive than the rasboras. When was the last time you added a fish to the tank? Its possible it introduced a disease and now there are casualties. What I recommend doing is holding off on water changes until next week. I would add aquarium salt (1 Tbsp per 5 gallons of water) as a preventative for now. Your plant will be ok with this salt treatment. Plants are not typically fond of salt, but java ferns are hardy and can handle the temporary treatment. I would discontinue using the Algae fix. Im not a fan of chemically treating for algae and right now it's something else in the water for the fish to deal with. You can medicate the tank if you'd like. Its hard to say definitively what killed your fish. I would do a basic parasite treatment. I like using Quick Cure which is a mix of formalin and malachite green. It works well for parasites and fungal infections. I wish I could be more help, but there are a lot of variables to rule out with only a couple symptoms. At this point I would add the salt, possibly medicate, but definitely monitor the fish for any other symptoms.Fish Suddenly Dying -- Help?!?They probably died of stress from the water change. When fish have gotten used to a medication for a long time, removing the medication presents a significant change in water conditions that can cause the fish to stress out and die, you have to gradually reduce the medication until you stop adding altogether. This kind of thing also happens to quarantined fish you think are fully cured and add back to the main tank.
