I would try to do the flush as it states. Then flush again with straight tap water all the way through, then take a handful or two of lime, if you can get it,...mix that around in the peat on the top, and then do a feed at 1/4 strength and wait 24 hours and see how they look. If all looks good, wait until the peat is a little drier on top and feed them with 1/2 feed. See how they look after another 24 hours. If all looks good, give them a 3/4 feed. That will be enough to finish them off. Don't go any higher.