I need some help trying to figure out a problem I have been having with my plumbing. For a few months, we have noticed that occasionally our water pressure seems to fall (shower pressure will drop for a few minutes and then jumps back to normal). We have been in the house for 18 years. We are on our second water softener (8 years old)

The only information I have on the softener is that it has Osmonics series 255 value/440 controller. (Did not get much information from the installer which is a different story - he also said having a regeneration based on water usage vs time would not make any difference and I use a lot more salt than with the old system. Also no hardness test results)

Sorry for rambling. Back on track - we are on city water. Neighbors have not noticed any problems. Anyway, my wife has been noticing a slight black ring develops around the commode. I opened the tank and found a black/dark gray scum at the bottom on about 1/3 of the tank. It was about 1/4 inch thick at the thickest. It looked like the black that leaches from the black rubber gaskets in the tank. I just stired it up by hand and it dispersed throughout the water turning the entire tank water black. We flushed it a couple times and put some bleach in the tank. (Same issue with the other commode)We checked my wife's coffee maker where it holds the water and that had some scum also. It is filled using water filtered with an under sink filter (chlorine/taste and odor).

We have a pool so I used the pool tester to test the PH and chlorine from both in the house and a faucet that is before the softener. PH is about 8 in both but the chlorine from outside is 1.2 (I assume ppm?) and nonexistent from inside faucet (unfiltered).

Any ideas of what I am facing? The water still feels soft so the softener is working. But, could the resin be filled with algae causing occasional water pressure drop? Is the substance we are finding algae or is it from the resin in the softener?

Any help would be appreciated.