The Natural Chemistry Instant Pool Water Conditioner (which is the same as Leslie's Instant Conditioner) has been around for a while as "Instant Pool Water Conditioner" and is sodium cyanurate in a slurry. It dissolves quickly into water so is a fast way to increase CYA. It is, of course, more expensive to use than pure CYA so it's a cost/speed tradeoff. If you only need to raise your CYA a little, you can use Dichlor for a similar effect since it also dissolves quickly and you can use that as your chlorine source and build up CYA over time. For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.