Phosphates?

[chem geek]

To add to what waterbear said, you have a couple of easy options to add CYA quickly. One is to use Dichlor since that dissolves quickly and for every 1 ppm FC added by Dichlor, it also adds 0.9 ppm to CYA. So using Dichlor as a chlorine source will help, but it will still take a while to add 60+ ppm CYA, but is something you can do in addition to the other option below (if you want).

The fastest and least expensive option is to get pure Cyanuric Acid (CYA). This dissolves slowly, however, so you need to put it into panty hose or a sock and hang it over a return flow. That way, it will dissolve in about a day, maybe two, if you keep the pump running 24/7 until fully dissolved. I suppose you could put it into a panty hose or a sock and put that into the skimmer (being careful not to fully block the water flow) as another option. Lastly, you could add it carefully and slowly to the skimmer (with the basket removed) directly and have it get caught in the filter, but that takes longer to dissolve (about a week) as the water flow per unit area in a filter is far lower than in the skimmer itself or from a return flow.

Richard