Who said Jiffy pots are bad? For seedlings I like those things they work better then Rockwool. You can wash off the roots and transplant them to Hydro or grow in dirt.
They are pretty generic and don't have any nutrients just stick with RO water through the seedling stage. Another thing seedlings like warmer soil temperature like in the 80's. A humidity dome helps to keep the seedlings moist. Don't over water only water when they are dry. Roots grow best when they need to work a little to find water. If you use Anti-wilt spray there is no need for a humidity dome. What lighting are you using and what is the temperature at the top of your seedlings?