No problem. Works just fine, dark or light bottle. Good at least 2 months. I also use a 25% APS stock also good for months - don't make it fresh. I am impatient, so I do a rapid polymerization: 10 ml gel mix (10%) 100 ul 25% APS 10 ul TEMED Pour, overlay with water, come back 5 minutes later. Ready to go. Kevin