[Nitram Draw]

That's 65 turns before your first converted atmosphere planet comes on line and more before they have any effect. If you can survive that long with the weapons you have you shouldn't be worrying to much.
If you can't hold that long I would delay the Converters and get to shields V. That is a lot more protection that shields II, which is what I think you have. Or begin researching some of the lower levels of the techs they have to get greater advances when you analyize the DN's you are going to capture.