Milky Stuff Inside Intake And Outtake PVC Filter Tubing

Hi,

A couple of months ago I changed the intake and outtake tubing for my Fluval 306 External Filter from the fluval ribbed hosing to a clear PVC hosing, as I wanted to add an in-line heater which required me changing the tubing. This all went swimmingly but I have recently noticed a kind of milky almost sediment like build up in the tubing, which is present in all the tubing and also in the air line for the air stone in the tank, although the water in the tank itself is very clear / not affected. Pictures attached below.

Has anyone heard of such an issue, a friend of mine said PVC can turn strange colours when filled with water, but I have also heard that it can be caused by fungus? I only started getting worried because I have probably 6 or so fish in the months since I installed the in-line heater, and I was wondering if it could be related.

Additional note: I have posted in fish health regarding a problem with my guppies could this be related?
Link: https://forums.thinkfish.co.uk/fish-health/need-help-identifying-what-is-wrong-with-my-neon-tetras/

I appreciate any help anyone could give me,

Thanks,
Nye


Water Parameters:
- Temperature: 24°C (very stable since addition of in-line heater)
- pH: 7.7 (I dont know if this is a bit high? but it is extremely stable so I have left it where it is)
- Nh3 (Ammonia): 0 ppm
- NO3 (Nitrate): 25mg/l (I change 20% of the water weekly)
- NO2 (Nitrite): 0 mg/l
- GH: 8°d
- KH: 6°d
- Cl2 (Chlorine): 0 mg/l