phostrogen feed, weed & mosskiller

Is there a better or more user-friendly preparation available which doesn't leave me with a blackened lawn? I've persevered with it for a few years now, getting the measures per sq. meter right, etc., but I still end up with those black lines. Would it be better to just give up on it and go back to using separate preparations for weeds, then moss, and then fertilizer?
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