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I had a school of 10 zebra danios going in my 55 gal tank
, they share with 6 emerald cories, 3 praecox rainbow, 2 SAE. moderately planted.
Now I have 6 danios and another one is dying. the other 5 are very healthy, no visible problems at all. THe dying danios appear to not eat???
All the other fish in tank are very health eating well and very active.
Any suggestions.
tank parameters good 0 nitrite, 5 nitrate, ph 8, ammonia 0.

What causes the ph to be 8.0? Was it sudden? If it was gradual, then the dying Danios were probably overly sensitive to the PH. try lowering the ph. but do it slowly. Drift wood is good for lowering PH gradually. But it takes a while.

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My Tanks at Photobucket

ph 8 is what the typical water here is at. This has been constant from the beginning of the tank.
typically 30% water changes weekly, use prime as the treatment.
tank is 5 months old.

Not eating could be down to stress or perhaps internal parasites.

What is the tank setup like? is it decorated or not, brightly lit or not, etc. As many details as you can think of will help to narrow it down. Temperatures filtration and oxygenation?

What is your feeding regime incidentally?

How do they act, are they schoaling, changing colour, thiniing at the stomach, are they bloated, or a bit pink anywhere, especially near the gills or stomach?

temp 75-76 F
feed: in the morning and in evening. VAries, tetra crisps(much loved) spirulna flakes every other day, frozen brine shrimp once a week, growing in tank snails crushed as they appear, green peas mashed about once a month, some freeze dried shrimp crushed to a powder once or twice a week.

Two large decorations and medium drift wood piece, medium amount of plants, low lights maybe 0.7 watts per gall.
@ HOB filter whisper 60 and marineland bio wheel 350.


Gills do appear red???
THe weird thing is it is only some of the danios several are big beasts(for danios) ???
I am guessing some type of parasite?
I thought I had lost another last night it was laying on side at the bottom of tank, kind of bent like a banana. When I tried to get it with the net it swam away and could not be caught. Went back late same thing. Well this morning it was swimming about, and when I got home from work it was swimming about. when feed this evening I could not really see if this one ate or not?
Still puzzled?

Could well be a parasite, the snails were probably the intermediary host that the fish picked them up from, try some jungle labs antiparasite formula or some sterazin by waterlife, and see how you go.

used some jungle labs medicated food over the last couple of days, the danio I thought would died is ok, but another one has disappeared. I think I forgot to mention previously that I have only ever found one deadfish the other 4 have just disappeared over night??????????

Well if there are really no remains at all , since you have no truly carnivorous fish capable of disposing of a large danio overnight I can only suggest that the fish are literally leaving the tank by perhaps jumping out, and perhaps being eaten by another family pet! Either that or theyve found a new and interesting way to get sucked into a filter.

What kind of filtration method are you using? Do check the water parameters as already suggested.

I have 2 hob for filtration, one marineland 350, one whisper 60.
check parameters once a week.
they always seem to be very constant really no variation at all.
30% water changes weekly.

into the second week of the treatment, 3days a week of jungles labs medicated food. Have not lost anymore danios, no bodies found anyway, but they have gone into hiding. Very difficult to get a count lately. there are several spot in the aquarium they can truly hide apparently bad set up I guess.
Anyway the one I though would die is still moving about may have gained weight.
there is no schooling action at all from the danios.

Well sad today down to 2 danios,and they have both gone into hiding. THe biggest danio I had was swimming about freely until last night when I found the second largest danios stuck to the filter intake. HE had been healthy, no torn fins, his gills were normal color not bright red. So I have lost eight danios now and only ever found two bodies?
I have no clue as to what is going on. All the other fish in the tank a fine and show no sign of sickness?

well final count lost 9 of 10 danios, all other fish in the tank with them are fine.

Thats a shame, it is possible that danios may have a strain of bacteria that they are especially suceptible too, or even more possible they may just have been a bad batch, they are widely captive bred, and if the parents were too closely related or of poor quality the longevity might have been affected. Natural spoilage in some species is very high when a little overbred. There may not have been anything you could do. Perhaps is was just a rough batch, happens sometimes.

If you want to replace the danios, try getting them from a different source and see how you go. TBH it sounds like you did all you reasonably could, and the keeping conditions were fine. Its frustrating when that happens, I sympathise.

wow, sounds like a real problom, something similar is happening to my tiger barbs. was your ph always 8 or has it draasticaly increased or decreased? also the bodys of the fish can tell you alot. theres a posibility of stress which is usually caused by to much waste or overstokcing but it will sometimes happen for no obvious reason. have you been making a lot of changes lately? if it is stress then check to see if the bodys are pale. that is my guess