I have some old trichlor sticks (2 years old). Are they still chemically useful. I thought of using them since my cya is finally down to around 30 or so (took 2 years of nothing but BBB for it to come down from over 100!). If they are still good, I could put a couple in the skimmer while I am gone on vacation (1 week) and come back to a pool with chlorine and a bit more cya. Is this a good plan? Thanks.