Not Sure What Else To Do

[Guest mariap]

I have had my tank for about 3 years, it holds 20 gallons and I have a ranchu and a common.

I use a whisper filter and have a gravel bottom. I feed sinking granules and occasional veggies.

I always use prime for the water and do water changes about every 10-14 days.

ammonia 0, nitrites 0 ,nitrates 20 ,ph7.2 ,alk 40, gh150

Last week Squirt had an area of slime coat that apeared thicker and red spots below his fins on his under side. I did a 25% water change and added melafix for five days then did a partial water change. He seemed better then red streaks appeared on his fins and his tail.

No new fish or any thing has been added to the tank since I started it up. The ranchu is fine, so far.

Squirt is swimming well and eating but today had a long white poop.

I started melafix and primafix.

What else should I be doing?

Thanks, Maria