I had a couple of sudden fish deaths last week which I thought were a one-off, but now there's been another...
15 gallon freshwater tank with live plants, been set up over 2 years
Ammonia 0, Nitrites 0, pH 7.2, temp 26 degrees centigrade, fluval U2 filter
Tank has a 10-15% weekly water change with the filter medium cleaned in old tank water. Substrate is largeish smooth pebbles, a sweep round with the net once a week gets rid of any rubbish on the bottom.
Currently 3 young fairly small weather loaches, 1 panda garra, 1 otocinclus, 1 black widow tetra, 1 white skirt tetra
In the past week I have lost 1 gold ram, 1 aged guppy and 1 otocinclus. I noticed that the ram and the guppy were missing last Tuesday, and found them at the bottom of the tank with no visible symptoms. They'd been acting perfectly normally up until the day before, so I could only come to the conclusion that something toxic had got into the tank or the live food they had eaten on the sunday evening had something bad in it. (I tested the water that tuesday, and the parameters were as above, which are the usual readings for my tank).
All the other fish were perfectly fine, so I added a couple of teaspoons of salt and put an aerator in the tank.
However, I arrived back from a weekend away today to find an otocinclus dead as well. He too had been as active as usual before I left- from the look of him when I found him I'd guess that he died on Friday or the Saturday. I had done a normal water change and filter clean on Thursday (I use water straight from the tap with dechlorinator)
I honestly don't know what to do as there are no symptoms to treat. The only thing I noticed was that even the fish who had definitely not been dead that long were smelly when I fetched them out, which I have not noticed with previous fish deaths. The water itself doesn't smell.
Any ideas?? I am planning to take some water to the LFS tomorrow morning and maybe buy some new dried food just in case, as we've had the stuff we've got quite a while. However as the otocinclus only eats algae I am not sure that it could be their food.
Is it possible that it could have been something in the live food (daphnia) that they were fed a week ago?
Please help, I am very attached to my fish!
BTW the guppy had been in the tank for just over 2 years, the otocinclus for just under 2 years, and the ram for maybe 3 months