Does my UV light in my SunSun canister filter render my Glut useless?
the short answer to your question is NO
Glutaraldehyde (glut) as a ~2% aqueous solution does not exist as the dialdehyde, but as the hydrate and as such it is not sensitive to UV light per se.
There are, however, many other factors to consider. While glut, when dissolved in clean water has a half-life of over 100 days, its half-life is somewhere between 8 -24 hrs. when added to an aquarium. The half-life depends largely on the prevailing pH in the aquarium. Glut is more stable under acidic conditions, but under alkaline conditions (pH 7 and higher) it is activated and reacts quickly.
It also dependents on the amount of plants that are in the aquarium. The more plants, the faster glut is consumed.
This then brings me to my question: both, the UV sterilizer and glut are used for killing microorganisms (e.g. algae, bacteria, fungi) that are floating around in the water column. Why would you want to apply both at the same time?