How'd the flush go?
You don't wanna use any soil that says feed plants up to x amount of weeks cause the soil itself has nutes in it that you can't control. Sometimes people say all the nutes can dump into your plant at once, sometimes your plant will get no nutes, and if you feed them nutes before all the nutes in the soil are used up or flushed out chances are it's gonna be too much for a little plant to take. As far as feeding you plants too young it's debatable. Most people will tell you not to feed a seedling until it's vegged for a full month. I didn't know that and started feeding mine at 2 weeks old. I started out with a very low diluted dose of veg fert. My plants never burned had any issues. (until recently I burned them just a little but they're over 7 weeks old now so no biggie) They took off from the day I started feeding them. I think the rule of thumb of feeding a plant at a month is a great idea but, if you're careful not to overfeed, I personally think, it's ok to start sooner.
Once you start feeding your schedule should be to feed every other watering. And you want to make sure that your soil dries out almost completely beore watering again. I'd say with like 10% of your moisture left if you can guesstimate that. You want the plant to believe it is in a drought time between waterings that way it produces more resin to protect itself and to get you higher.
If you're gonna keep feeding now I'd say like 1/3 to 1/2 TEASPOON of fert to a gallon of water. Do that for 2 feedings or 4 total waterings, then up it another 1/3 or 1/2 TEASPOON, do that for 2 feedings/4 waterings and then up it again. Continue to do this until you see the very tips of your leaves start to yellow. Then back off of fert a little bit. By that time you'll have a feel for what you're doing and should be able to read what your plants need.
The Key with feeding seedlings is to start with a little and go up in very small incrimints.
Hope this helps bud! Good Luck!!