Hey brother! In my opinion, and beeing right true with you, fuck jiffys bro. They just bring trouble to the little seedlings. And you can see that by now ;) You have some burned seedlings, probably cause the acid ph that they bring, and thats not so good in this stage. And I see some other things you shouldn't do. 300w for seedlings bro... is too much light. They don't need all that amount, and you're just spending money in electricity that you dont need to spend by now. Some t5s will do the job till the plants have some 4 pairs of leaves. Another thing... NO nutrients by now. You can kill them with an hell of a burn and your soil will have the nutrients they need now. You can cause a lot of stress on your little seedlings and they cannot handle so much trouble... Take care mate. Any question just ask ok? People are here to help and share knowledge :) Keep it up mate, take it easy ;)