Hi Devs, thanks for the welcome and reply. The white spots on my black moor's (Robert) top fin disappeared today, but the 2 white spots on his tail appeared kinda flat today. I also noticed on the left side of his body there's a white spot, it's like the size of this ( )

sorry i don't know how to tell you the size so i use ( ). I hope you won't mind. The test results are here
Ammonia Level? 0
Nitrite Level?0
Nitrate level?20-40
Ph Level, (If possible,KH and GH and chloramines)? 6.8 the ph is low, can I add sodium bicarbonate in there to increase the ph lvl?
Ph Level out of the Tap? 6.8
Tank size (How many Gals) and How long has it been running? 20 gallon, for 6 months
What is the name and size of the filter/s? whisper 40 and whisper 30
How often do you change the water and how much? 2 times a week, about 30-50% each time.
How many fish in the tank and their size? before i added the 2 new goldies I have 2, but now i'm overstocked with 2, so I have 4 now.
What kind of water additives or conditioners? API's stress coat
Any medications added to the tank?no
Add any new fish to the tank?yes
What do you feed your fish?Hikari oranda gold, Hikari wheat germ, Goldfishconnection.com's freeze dry blood worm and their spirulina flake, and regular peas
Any unusual findings on the fish such as "grains of salt",
bloody streaks, frayed fins or fungus? I'm not sure
Any unusual behavior like staying
at the bottom, not eating, ect..?sometimes bottomsitting, but eats well and swims normal.
I really love Robert, he's so beautiful I hope he's alright.