It has a lot of calcium and magnesium carbonate so it ok that rises the ec up, 300/400us are fine, 300/400ppm are a little bit too much, you can flush a little the soil. If u are experienced ph issues on the initial stage of the grow you have to change your soil cause maybe is pretty shit, i go over all flowering with no ph issues adjusting ph only when i give nutrients. Using biobizz light mix