Help... I'm Not Sure What I'm Doing

[splash]

Hiya, i'm new to fish keeping and up to now i'm not doing too well!
My tank has been set up about 3 weeks (hadn't heard of fishless cycling and just went by the leaflet in the fresh start/ filter start kit) It's a 68 litre juwel, given to me second hand. Not used for approx 4 years. Reused gravel but did wash it thoroughly first.

Got my first fish (i cringe when i say this after reading all your info) on day 9.... 5 zebra danio
After three days one died. Noticed a white patch on another, first noticed as soon as we got home. Didn't look like a spot or cotton wool. White patch got bigger and fish was obviously unwell. Asked for advice at LFS who said to do 50% water change and add some salt. Not to add any medication until water stats were better.Ammonia was a bit high. Did all that...fish died!

Noticed similar white patch on third fish. Went to a different LFS who was horrified i'd changed water by 50%, told me it sounds like bacterial infection as 2 fish are unlikely to have an injury which would cause fungus. Sold me some Myxazin, also bought a Nutrafin mini master test kit (liquid type).

Took out carbon filter and started medication (still adding filter start every other day)Now on day 4 of 5 day treatment. Fish is still alive but goes through phases of staying near surface and keeping away from other two. Didn't think he'd make it through the night but he's still going. Doesn't seem to be eating much either.
Checked water tonight before i put in medication...

Nitrate 20/50 (Hard to tell which colour)
Nitrite 0.8
Ammonia 0
PH 7.5
Need advice please on if there's any chance the situation can be rescued.... before i kill all my fish or the stress of it all kills me!

 

[WILDER]

Water changes and increase aeration in the tank as bad water quality makes it hard for fish to breath.
Just add the correct amount of med back to the water removed.
Sounds like the lfs thought your fish had columnaris.
Columnaris has so many disguises. Can look like cotton wool, strands of cotton coming of fish, bleached out white patches.
Does the white patches go along the back and down the sides to form a saddle shape.

If you only have danio in the tank I would add some salt as it helps fish in a cycling tank.
Just for now add one tablespoon to a jug of tank water and stir till it disolves. Then add it to the tank.

 

[splash]

Thanks for replying so quickly....

The white patch does look kind of saddle shaped. Moreso on the last fish that died than this one. Patch starting to look a bit pink now. Last fish also had white stringy thing that you mentioned, although i've not noticed any on this one so far.

I've got a large air disc in tank already. Had an ornament standing over it so i've taken it off to release more bubbles. Just added some salt. He's now looking really poorly. Seems unable to swim straight, head keeps floating upwards. Might help if other fish didn't keep hassling him! Haven't got anywhere else to put him so guess it's fingers crossed he makes it.

Is this likely to spread to the last 2 fish as well?

 

[WILDER]

Columnris can come in the colour of pink as well, brown, yellow, white, greyish white, pink.