As Spimp says, we need to see some pics. I'd be surprised if week old plants have any deficiencies though, they don't really uptake nutes at that stage. Maybe strictly a ph problem? I fight with those myself as well as hard water issues.
You might also want to take a look at New Member Start Links which have lots of good information about posting and navigating the sites. And FAQs is a great place to look for answers and ask questions.
Great to have you onboard Vlad! Have a canna-tastic day.
Vlad, great name! Looks like you have already got some good advice, any deficiency is unlikely at that young age. I also use ro water (distilled) for seedlings and it works great for me. Your pic looks kinda overwatered. Remember to let them dry out good between waterings (and they don't need much water right now to begin with).