Can you dose the cal-hypo into the skimmers to have it dissolve on the sand in the filters? If you do, be darn sure the chlorinators are on the outlet of the filter and there are no other chemicals before the filter. Cal-hypo can mix with dichlor and triclor and CYA to go boom.
Try swapping the inlet lines between the chlorinators and see if that moves the problem. If so, maybe it's the tap or a crushed line on the inlet side. If the problem doesn't move then maybe it's a similar problem on the outlet side.