Most test kits you can buy at Walmart, etc., will only show chlorine up to 3.0 or 5.0. To be able to test higher levels than that, you need a FAS-DPD test kit like the one Ben sells at www.poolsolutions.com. I don't know what your local pool store might sell in terms of kits. Maybe they have a FAS-DPD? Just be careful at a pool store and don't buy everything they might try and push on you.