HMM. I am in my 5th week of flower and have been feeding them around 1100 ppm since 3 weeks before flip, I never have to correct for buildup. I would think if your medium is retaining so much that you are not getting enough runoff every day or you are letting your coco dry out which will cause the salts to dry out and build up. That is why coco users are to do sufficient runoff every day, to push the salts and such out while replacing them with new food. You could lower your feed to say 200 PPM, flush out your coco until you get around 200 PPM coming out and than just give them a normal dose of nutes. Carry on from there but if you are getting that kind of buildup in your coco you need to get more runoff every day so you don't get the buildups you are getting IMO.