A great product designed especially for goldfish.
"Gold Buffer is a non-phosphate buffer that will maintain the ideal pH for goldfish while not enhancing algae growth. Depending on dosage, GB raises and buffers betwen 7.2 and 7.8. It is gentle, safe and enhances the freshwater environment. It is compatbile with all other Seachem buffers. Contains sodium, potassium, magnesium and other bicarbonate salts.
The reason I prefer to use a commercial buffer, in particular Seachem Gold Buffer, over crushed coral/baking soda combination is that this product does the job of both. Baking soda is easy to dose with, however the alkalinity is soon exhausted. If relying on crushed coral to increase alkalinity it will only dissolve once the pH drops below 7 so there could still be a lapse and a significant pH drop while the coral dissolves and does it's stuff.
I have used this product in all my tanks and the outdoor tub for more than six months and it is reliable. I didn't change the water in my outdoor tub for 4mths over winter but the pH remained stable.