I second Nicholas here; your stains are coming from developer being carried over into the fixer. You should always use fresh, strong stop bath (short stop) with fibre-based papers to ensure developer is not carried over into the fixer. Take your time, make sure your print is fully immersed in the liquid for the prescribed time. Make fresh stop bath for each session; or at least discard ~25% and replenish. If you've no stop bath to hand, use strong vinegar at a pinch. Also, make sure you either wash off or immerse in stop bath any tongs or fingers you use to transfer prints between the baths. Stop is cheap and good paper is expensive; using a stop bath for printing will save you time, money and frustration in the long run, a lesson I learnt over many years!