It's perfectly normal for a pool to lose all chlorine in a brief time, when there's no chlorine stabilizer (CYA) in the water. And, until you begin using the dichlor, there will not be any stabilizer. As long as your water is clear, there's no need to 'over-dose' -- by doing so you risk bleaching your liner. The effect of chlorine on liners is MUCH greater when no stabilizer is in the water.

Just make sure you treat it in the evening, rather than in the morning. That way, it will be able to 'work' all night, before the sun hits it. Also, add a single dose just before each use.