Help Common Goldfish has Red patches on gills

[Bob4426]

so my tank is was very clean and clear however , the guy at the fish store said change 25% of the water every 2 weeks and so i did and the tank became greener and greener , so i take out 20% every 3 days to make the tank clean and today i just noticed one of my older goldfish's having a red patch on his gills and im very worried , how long does he have to live and what is it caused by ? how can i treat him ?

 

[Aspen35]

so my tank is was very clean and clear however , the guy at the fish store said change 25% of the water every 2 weeks and so i did and the tank became greener and greener , so i take out 20% every 3 days to make the tank clean and today i just noticed one of my older goldfish's having a red patch on his gills and im very worried , how long does he have to live and what is it caused by ? how can i treat him ?

Cn you start by filling this out please? I can start by telling you right off the bat that 20% water changes will not serve you much good. continue with water changes, clean water can help the fish stay healthy or get better. With every water change, tank another 10 percent ish out. Eventually, you can work your way up to 75% -80%.

Tank size:
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tank temp:


Fish Symptoms (include full description including lesion, color, location, fish behavior):

Volume and Frequency of water changes:

was the tank cycled before you added the fish?

Chemical Additives or Media in your tank:

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Recent additions to your tank (living or decoration):

Exposure to chemicals:

Digital photo (include if possible):