Sudden Tetra Deaths

[birdiefu]

I have had three Glolight tetras in my quarantine tank for weeks now. Original problem was that one had a tuft of fungus above it's eye and I took him and two buddies to keep him company out of the main tank to treat with Maracyn Oxy. Followed the directions on the bottle and treated for 5 days. The fungus receded on the one fish, and over another week it healed up fine (white patch turned to a shiny patch, then turned to "normal" skin aside from a little crater where the infection used to be).

I was about to put them back in the main tank when that same fish got another white patch starting on the other side of his body above his gill. The other two fish never showed any problem, and even the infected fish acted and ate fine the whole time. So, I started another round of Maracyn Oxy two nights ago. Put my second dose in last night, and today when I went to feed them, no one came swimming up, they were all toast. Only thing different I had going on in the tank was that I had installed a power filter on that tank earlier in the day when I started the meds again, it is in addition to the sponge filter that was already in the tank.

I am confused as to why all three went to the big tank in the sky all at once when they had not had problems with that medication prior, and it was well over a weeks since they were last treated. What should I have done differently? I was under the impression that the fungus was probably from an injury and tank cleanliness (I was doing ~40% water change 2x/week), which is part of the reason I added a second filter after seeing the fungus on that fish again. Should I totally disinfect the tank and get rid of the sponge filter that could be harboring infectious disease?

Any input would be appreciated, I feel like it was my fault that they died and I don't want to kill any more poor fishes.

 

[Atrixblue.-MFR-.]

you dont need to dis infect the tank a good empty and water only clean would suffice. only thing i can think of is that the filter is more powerfull than the other and undermimed the established filter thus sending the water quality down hill sharpish, does the new filter have carbon by anychance, carbon will filter out the meds you put in the tank making them useless. did you rinse out the new filter media just incase there were factory contaminants on them? no need to clean the filter either as the meds would of taken care of the fungus while circulating in the filter. its not your fault really, its just a learning process.
how long have you kept tropical how old is your tank and fish in them. how big is the tank. how many fish do you have in the tank(s) have you tested water quality. do you dechlorante the water on every change partial change?

 

[birdiefu]

Thank you for the reply! My main tank is a planted 29 gal with 7 danios, currently 4 glowlight tetras (was 7, guess I need more now!), and 2 pearl gouramis. It was started on a fishless cycle in August, finished around Oct, and I have been slowly stocking since. The tetras were added last, first put in about a month and a half ago. The sponge filter for my quarantine tank was cycled with the main tank, and has resided in the quarantine tank since. I have had no sick fish before this.

I use 1/3 RO water and 2/3 treated (stress coat) tap for every water change, and I just checked ammonia and nitrite in the quarantine tank and they were both 0. I was under the impression that since Maracyn Oxy was not an antibiotic but chlorine oxides, that the carbon would not affect it, however I could have been wrong there. I did rinse the filter media, but not the filter housing itself...perhaps I should have with those "new plastic" chemicals on it? Oh, and the quarantine tank is a 10 gal that only had the three tetras (and some snails).