Seedsman Alaskan Purple

Using half strength general hydro on all plants and they were all taking it good until about last week when my Alaskan purples started "clawing". I flushed it tight away but it seems like it only slowed the process. I'm not sure what I should do at this point. I'm currently just giving it dechlorinated tap water. hopefully this fixes it? Still growing but definitely falling behind other plants.