Tropical fish Scale discolouration and died

[ShinojFez]

Buddiez,
I had an angel died post two days after witnessing some scales discolouration. This happened on 26th April.
I thought it’s due to some desease and changed water (60% of total capacity), then it was okay for some weeks until I lost two of my dwarf gouramis on 25th May with same symptoms.
Photos attached for your valuable inspection.
I’m worried about the rest of the occupants.
Tank conditions mentioned below:-
76Ltr tank with original plants, 20% water changing in every two months.
Tank is going to be on year old.
Please help !!!
Thanks
Shinoj Fernandez

 

[Aiken Drum]

Please take a read through the "unhealthy fish" sticky and give as much detail as you are able.

https://www.aquariumadvice.com/forums/f17/before-posting-about-unhealthy-fish-read-this-32451.html

On the face of it a 76 litre tank isnt big enough for angelfish and 20% water changes every 2 months isnt anywhere near enough. Living in such unsuitable conditions will lead to all sorts of health issues.