Rasboras - Harlequin losing them fast

[Ob1]

have changed water today 10-15% after taking some test

Current - Last Week
PH 7.60 - 7.60
Nitrite 0.10 was 0
Ammonia 0.10 was 0
Nitrate 50.00 was 5 double checked....


please any idea, will all my fish die??

 

[Ob1]

1. Water parameters. (ammonia, nitrate, nitrite, PH, temp', Hardness etc)
see above
2. A full description of the fishes symptoms.
skimming the top of the tank

3. How often you do water changes and how much.
twice weekly 15/20%
4. Any chemicals and treatments you add to the water.
ich treatment after new fish added

5. What tank mates are in the tank.
see below

6. Tank size.
see below

7. Finally Have you recently added any new fish?
3 Rasbora 1 died from fungus 1 died yesterday showing symptoms above
2 adults dead today aged 5 years.