why isn't blood acidic, given that carbon dioxide in the blood is converted into carbonic acid?

The balance is maintained by buffers in the blood such as indeed bicarbonate, and also ammonia. The next system is the respiratory system. Any decrease in pH is detected by chemoreceptors in the medulla oblongata and stimulates a faster rate of ventilation. This results in a more carbon dioxide being blown off, which raises the blood pH back towards normal. And vice-versa. The final system, which is the slowest mechanism but also has the most capacity for regulation of pH is the kidneys' ability to excrete excess acid or base.

The pH value of the blood is maintained due to several conditions existing in the blood itself.In short, blood has a great affinity for oxygen and continues to form oxy-haemoglobin during the process of respiration.At the same time when the carbon-di oxide released due to the above process is transported by the blood itself to the kidneys for eliminaton.Moreover, exhalation of corbon dioxide during respiration also helps in maintaining the pH levels of the blood.