Always ph your feed, especially with soilless mediums. Depending on how heavy you feed them and what size cube/fabric pot you should do an EC check every week until you are comfortable with your methods...and you should probably ec check runoff anyways.
If you feed at 2.0 ec your runoff should be between 2.8 and 3.5...anytime yout runoff is higher than 1.5 above input you can run into lockup or burn