I was asked in a PM about Cyanuric Acid solubility, but thought I'd put this into a Deep End thread so others can see the answer.
The chemical structure of Cyanuric Acid is seen here, but that is when in water where it can go back and forth in two forms, though in practice the acid form on the left releases one of its hydrogen atoms into the water so that the dominant form at pool pH is the cyanurate ion (singly charged).
In solid form, Cyanuric Acid has the form with the ketone (with double-bonded oxygens; known as isocyanuric acid) and as shown here it forms strong hydrogen bonds between the hydrogen attached to the nitrogen and the oxygen (i.e. NH:::O hydrogen bonding). This is what makes it relatively slow to dissolve since the hydrogen bonds are reasonably strong (and there are many of them) so take more energy to break apart. Putting the cyanuric acid into a sock or stocking and hanging it over a return flow or in the skimmer helps it to dissolve more quickly.
If one adds a strong base to Cyanuric Acid, then one can form a sodium cyanurate and this is what is done in the Natural Chemistry® Instant Pool Water Conditioner product which is the sodium salt of cyanuric acid (i.e. sodium cyanurate) in a slurry so dissolves much more quickly. It's about twice as expensive as pure CYA for the same CYA level, however.