First Fish Death

[Maxamus]

ok ive had my fish for about 1week today. I have done my fishless cycle. On the weekend (saturday) ]i bought to new angel fish to go with the 2 silver sharks, 2 opaline gouramis and 2 golden gouranis i already had. for the last 2 days i havent seen one of the angelfish and today when i got home i found ones dead body. I seem to also have a large amount of green algae on my rock that is extremely hard to scrub off. Do you guys think i have a disease or something and what immediate actions should i use to protect my tank.
PS I have a 130liter tank with aqua nova 1500NCL external canister filter as well as lights air pump and heater. My water temperature seems to be stable at 23-25 degrees celcius.

 

[Maxamus]

ok just measured my levelsthey are
Ammonia: 0
Nitrite: 0
Ph: around 7.4
Nitrates: 20

 

[WILDER]

Added to many fish to soon.
Silver shark are bala shark and shouldn't be kept in tank less than 75 gallons.
Any symtoms to go on with the angel.

 

[vinylman]

Angel fish aren't great choices for a new tank, even one that's cycled. Like most Tetras, I wouldn't add one for a good 5-6 weeks after cycling has finished.