Water Evaporation??

[halcyon]

So I've been running my WC kit for over a year now.. it was basically an innovatek kit with the eheim pump and the little reservoir plugged into it then run through rads etc etc.. anyway I've had to put some more water into it a couple times, not tons, but a couple ounces at least.. is that normal? I was thinking a sealed system wouldn't evaporate.. apparently I'm not entirely sealed?

[HeThatKnows]

Water vapor can diffuse through the tubing walls. Silicon tubing will lose more, the vinyl based stuff you have loses less, but any flexible tubing will let some water escape.