You need to test the water. MG soil is always on the acidic side because of all of the additives they put into it which is why it's a poor choice for our uses and has been mentioned as one to avoid countless times on every grow site. And adding ferts to MG soil is a very bad idea, especially when the plants are seedlings and shouldn't be in such rich soil in the first place. All the water you've been adding will only increase your problems as the roots need to breathe and also the excess water will "open" the time-released ferts to only add to what's already in there!