Some of norprene is made of rubber, I don’t know about this specific one. Just like tires, eventually rubber gets old, cracks, begins to break down. Most peristaltic pumps I have used have a relatively flexible, clear or opaque tubing within the pump. I would discuss with tubing or pump manufacturer, and come up with tubing at does not break down. I seem to remember ordering nalgene clear tubing for lab work, or included with some instruments employing peristaltic pump.

I concur with William F. Hansen . I've used peristaltic tubing that is either off-clear or black. (I'm thinking of a pump to, say, pump out a sampling well, say 1 gallon per minute.) The tube gets beat up by the pump, so it is important to get appropriate tubing and tubing that isn't too old. Also, you don't want tubing that might leach anything into your sample. You might see if there is an appropriate off-clear type if the black is giving you problems.

[In realty, if you are filtering the resultant samples, some little black flecks might not affect anything if the tube is of the appropriate material. But I'll leave such a thing to your professional judgement. I'd still start with new tubing. It really shouldn't be crumbling during use until the tubing is old.]