I've found that Feser One dyes gunk up your look if you keep it longer than a year. I had that in my old loop and i had to clean out everything and brush it down.
I currently use PT_Nuke PHN and Distilled water I bought from a local water shop. They claim it to be 99.9% distilled, which is basically hydrogen + oxygen, with no additives. I drain my loop every 6 months and wash it out with diluted vinegar every *other* 6 months.
I've taken apart my loop, and have found it to have minimal to no gunk.