For a clone with roots I would start with around 350/400 PPM and keep an eye for yellow tips on the leaves. some plants can take a heavy feed while other will burn at the same PPM, but 400 should be fine.I increase my PPM weekly until I reach a peak of around 1200/1250, and then I go backward for the last two or three weeks. The PH problem is probably a nute or medium thing, but if you know that your PPM going to drop that much, I would adjust my PH to 6, which is an OK measurement. 5.4 in my opinion is too low, I would aim for 5.8