I use a moist jiffy cube, and always water it on the saucer, so the lower part of the cube is more moist than the top which i think encourages the seed to root lower in search of the moisture. If the shell is not detatching itself, i would use a sterile set of tweezers to remove it, gently though, if it doesnt come away easily leave it another day or two and try again. I have never used happy frog soil, but i started a jiffy cube with a small seedling in it in a bigger pot with biobizz light mix, and the soil was too fine and it was easier for the roots to push the plant up out the soil than it was for the roots to grow down. So i had to repot and backfill so the plant cotyldons were sitting flush with the soil just so it would support it enough to allow the roots to grow down and anchor in. I only use LED's and i have never had an issue. Hopefully its just bad luck with the seeds. What type of seeds are you using?
