This is what happens to tubes that can’t be deep cleaned, and is largely why cheaper machines are discarded. Look at the mold in this Tyent!
Some companies try to brag that their water ionizers never need cleaning. What they're not telling you is that their machines cannot be deep cleaned, and mold will eventually build up in the lines, and can make a person sick! Please have a look at this video... Dr. Michael (who has owned and tested several different brands of machines) said he found mold in the lines of the cheaper machines. He said will never buy an ionizer that can't be cleaned, and he has good reason to say this!
