Why are my goldfish dying??

I am relatively new to the hobby. I just set up a 55 gallon tank about 4 months ago. It was cycled before I added my fist batch of fancy goldfish. Unfortunately one was contaminated with ich and all but one died. I bought two new ones (plus the one I already had). Two Orandas and a ryukin (all small) from a reputable online breeder and they lived happily for about a month.

After a 20% water change this weekend one suddenly couldn’t swim and just floated around the tank. He died one day later. Now another is showing the same symptoms. Just floating not even attempting to swim or eat. I have checked the water parameters and all are fine (except for ph which is always high: around 8.5 but it comes like that from the tap.)

Why are my fish dying? I am really disappointed as I have lost two batches of fish so far. I would love to save my last one but I’m not sure what the cause would be.

 

What is the temperature of the aquarium? Goldfish prefer cooler water, so large fluctuations in heat could kill them.

Also, they prefer the PH lower I believe as well (someone please correct me if I am wrong). There are ways to lower it, I have used vinegar to do this , or you could use almond leaves, which has other benefits as well. The most important thing is to make the change gradually, otherwise they could die as well. Everything needs to be carefully monitored.

 

Temp is room temp. I do not have a heater so between 60 and 70 throughout the day as the room temp changes.

I’ve tried almond leaves, Pete in the filter and driftwood. All of which turned my water a lovely shade of brown and had no effect on my PH. I still have the Pete and driftwood in there (for about three weeks now) but my water ph hasn’t budged at all.

 

Can you list your actual ammonia, nitrite and nitrate readings?

 

Ammonia - 0
Nitrate - between 0 and 20 (as of this morning when I lost my 2nd fish)
Nitrite - 0

 

Those number are great, so obviouly that's not the problem.