For everyone else, cheers for the advice.
It is a black ibc tank that i have outside, and under some shelter. Which i thought would help prevent algae etc from growing inside. I purchased one that was a manufacturer's reclean standards (of ibc tanks).
My ro i keep indoors and feed into tank thats just beneath the window, outside.
Im due to change the pre filters so will check all containers etc then. Thanks.
I do flush my system for about 10 miNs before i use if every time. I thought that would clean/prevent any internal build up of germs etc?