Transplant them into the Scott's, asap, because that MG is killing them. IDK whether it's acidic, or what, but it just looks plain unhealthy, and the plants aren't liking it. It might be okay for bigger plants, but doesn't seem to do the trick, for seedlings. It doesn't even look like soil, it looks like wood chips.lol Anyway, it doesn't sound like you are overwatering or underwatering, so I'd say it's the soil.(as long as your water PH/PPM is okay)
Does the Scott's actually look like soil?lol I've never used it, but will recommend that you add perlite to it before using, especially since it's labeled "moisture advantage". That's pretty much telling you that it holds moisture well, which isn't desirable for growing cannabis. Add at least 10% perlite(20-25% is better), or there will be a good liklihood that you'll run into overwatering issues, and possible premature acidity, due to the soil always being damp.