mysterious deaths

[cutechic]

i had one black neon and three golden danios in my 5 gallon tank. the black neon was extremely lethargic, and the danios gasped at the surface of the water several days before and up until their death. they all isolated themselves and didn't eat. i performed two water changes in the couple of days before their death, but their health didn't improve. eventually all four fish died. one thing to note is that the three danios' throats looked like they had been split with a knife (sorry, thats the only way i could describe it); other than that, i could see nothing wrong with them, but im not expert. here are the water parameters at the time of their death
pH: between 6.8 and 7 ppm
ammonia, nitrite, nitrate: all 0 ppm
KH: 4 degrees dKH
GH: 3 degrees dGH

another black neon and two white clouds were in the tank at the same time, but they never got sick, and are still healthy today

 

[-=DG=-]

Sure they are cuts ot just bruises or veins. When my malawi are holding, their throats look a bit like that. Maybe from over gasping theywore out their throats?

 

[Jamnog]

was the cut sort of vetrical on the side of the fish like their gills had been pulled back? as for the gasping do you airate your water?

edit : do you have live plants?

 

[cutechic]

i dont think it was just a vein in their throat. none of the fish that have died previosuly looked like that.

yes, the cut did sort of look like the gills were pulled back

i didnt airate my water at that time because my lfs told me that the filter (wet/dry w/ biowheel) airated the water enough. after the fish died i got an air stone, which may be why my other fish survived.

and no, i didnt have live plants

 

[reg2k2]

Higher temp's will lower the oxygen content of the water.

 

[cutechic]

hmm. . . this happened in the winter, and before i got my heater, too, so i dont know if thats why. could it be some sort of chemical that got into the water that disappeared after a water change?

 

[Dragonslair]

How big is your tank? As in length times breath. Many aquarist have large depth tanks saying that they have a 2 gallon tank or a 200 gallon tank. I have a friend who has a 200 gallon tank, but it's only 15" long by 12" wide, the rest is made up by depth. He does have super airation in it though. The tank can be shallow to keep fish in but it's the surface area that is important. This allows for diffusion of air to the water.
When an airstone is placed in a tank, it's not the bubbles that the fish breath, although many people think that. What the bubbles do, when it reaches the surface of the tank and bursts it increases the surface area of the surface water allowing for more rapid diffusion of air to the tank. Dissolved air is the exchanged with the carbon dixoide at the surface. Therefore the more airstones, the finer the bubbles, the more diffusion that takes place allowing for more oxygen to get into the water. Here endeth your science lesson for today.
It does sound like oxygen deficiency. Were the "cuts" bright red or were they dull red? The reason I ask is that if it was bright, then it's not a matter of air, but maybe chemical; if it was a dull red that it is probably air defiency.

 

[Jamnog]

mm dragons right it tho you forgot that while under water the surface of the buble adds to the surface aria too and while under pressure of being under water the effectivness of that surface aria is increased. heh meanwhile i think adding plants would be a good move even if they are free floating ones. they will help the fish in many ways other than just looking nice and a bunch will normally just cost a couple of pounds.

 

[cutechic]

i know, i didn't know about the benefits of a large surface area when i bought the tank

and thx for the lesson, dragonslair, ill remember it!

well, each side of the hexagon is around 7", and the tank is 12" tall

yes, the cuts looked bright red, not dull at all.