Also keep in mind that the CYA dissolves VERY slowly and can take up to a week or more to completely dissolve and reflect accurate test levels. Don't add more CYA or backwash your filter for at least 4-5 days. Remember that it's much easier to sneak up on your target CYA number than it is to overshoot it, because drain/refill is the only way you're gonna bring it back down...

Janet