Mana Channels, on the other hand, were arteries and veins that connected the mana core with the rest of the body. Normal people had them sealed, which meant that they weren't used. Having them sealed prevented mana from passing through them, which would be detrimental to a magician. Once a person started studying magic, he or she would unseal them. How? By ramming enough mana through them. This was the standard way of unsealing mana channels used by the Magic Academy. There were risks to such an approach. By using brute force like this, the mana channel of that person would accrue debris and would sometimes even have the mana channel blocked. There were, of course, ways to remove the blockage, but they were expensive and painful. A mana channel with debris made the movement of mana subpar, or even ineffective. This was the reason many magicians were slow at developing their craft, or would sometimes even be hurt by merely practicing magic.
There were other ways to unseal a person's mana channels. They were way more expensive and hard to acquire than simply brute forcing them. Noble lineages had their own ways of unsealing their mana channels, many of which were vastly more effective than the methods used by the Academy. This put the nobility high above the commoners in terms of mana channel development.
There were many ways to increase your mana purity and mana capacity.
To increase a mage's mana capacity, he needed to calm his mind. Then he would extend his senses out of his body and feel for the mana in the environment. This was what was called external mana. After that he would extract the mana from his surroundings through his mana channels, all the way until that mana reached his core. Once it reached his core, the mana would be assimilated by the already existing mana in the core, the internal mana, therefore making it his own. The act of absorbing mana like this was called meditation, and it was standard of all academy students.
The main way to purify mana was compression. When a mage had enough mana in his mana core, he could fold the internal mana upon itself, compressing it further and further. The more it was done, the purer the mana became.
There were other ways to increase the purity of a person's mana, such as by pills, artifacts, and treasures. A convenient way to increase the mana purity was to have pristine, higher grade mana channels. If the technique to unseal the channel was good enough, it could even upgrade the mana channels so that when mana passed through them, it was automatically purified. There were even treasures and pills that could even upgrade the mana channels so that they could purify mana more efficiently. Of course, compared to manually compressing mana, the effect was negligible. The main way to purify mana would always be compression, with mana channel purity second.