White stuff coming out of the return on filter?

[BigBlue]

Everytime I refill my filter and restart it I get a white flakes coming out of the return. I running a FX5 with duel Bio-wheel and UV split off from the return line......Any Ideas?

[waitaki]

same happens to mine I also thought it to be slime that accumulates in the pipes it goes back up through the filter soon enough. Doesn't appear to be fatal.