Hiya V12|V12,
This is my first post in this forum - I've lurked for a while but since I just recently had the same problem as you with the 'white stuff' on the inside of my tubes I thought I'd post.
I have an eheim 1250 with an evaporative type setup - large res with high surface area, so my loop is not closed (pseudo bong type of setup - reason i do this is I'm prepping for a chiller I'm building and the res will contain the evaporator - then it will be closed)
Anyway, every once in a while I notice my tubes getting clouded up with that white stuff - if I squeeze the tube the pump pressure clears it away in that spot but generally it just seems to build up over time.
I tried jet dry and like you it did not clear up the problem (it did make my water smell nice
- I don't use additives normally since the evaporation would make the room hazardous.
So I figured what the heck - I poured some generic supermarket non chlorine bleach in and let it run for two days - poof crystal clear again, drain - throw some more jet dry in and all set for another couple weeks.
I'm inclined to think the white stuff is mostly biological - maybe keeping the water chlorinated like a pool would help, I may try that but have been wondering about the effects of bleach and chlorine on other components (tygon especially)
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Enyin, Water Cooling Nerd!