The stix only show purple when there is an overflow of ketones from you blood. Being in ketosis means that your body will not turn excess ketones into fat and simply excretes extra ketones in your breath and urine. Just becasue you don't show positive on the stix doesn't mean your not in ketosis. It may mean that your body is using all the ketones it is making and there is no excess. If you work out a lot then your body may be using all the ketones being produced.

On the other hand...it is better to test in the morning..because at test strip will also turn purple when your body is buring up a fatty meal. The strips have now way to differentiate between fat you've eaten..and ketones your liver has produced from your body fat.

I hope this helps and wasn't confusing. I've done sooo much research on ketosis.