Urgent! Sundenly Green Water Colapsed During Water Change Options

[Donny041280]

Hi there,
I just recenly change my green water (green water) 80 % then it's started to get clear water (CW) on the side of the tub and many green flakes floating around and started to sink in the bottom, is it normal? ( i havent get this problem before (already changing around 5 times)

My data:
A. Around 110 litre plastic or fibre tub (i don't know lah )
B. 10 2-3 inch oranda and ranchu (overcrowded)
C. Full sunlight, on the top i just use small hole plastic ( just like the one to repel insect) to limit the sun rays
D. I usually change water every 2 day, coz with full sunlight the water become green vey fast (almost black in the middle)
E. Feed 4 times a day every 3 hours
F. At day air pump small output, and at night i use full power
G.my well water is acidic PH below 6,4
So i use BS to get around 7,8 to 8,2

My method of changing green water:
1. Syphon all the green water to 80 %
2. Start pouring water (well water)
3. At 40% water i start to put half tea spoon bicarbonate soda (BS)
4. At 80% put another half tea spoon
5. Done

My question
1. Is the green flakes floating and sinking after WC, normal?
2.if not should i quarantine my fishes immedietly?
3. Is my method of changing green water correct?
4. Are there any flaws with my method, number of fishes, feeding, aeration, etc..?

Thank you very much and looking forward to receive knowledge from the all the master goldfish in this
Great forum )