Hi. I'm on week 3 cycling, got a fluval skimmer which will cope with 200 litre..mines 120 litre. I'm struggling with the cup position. Right up high and no foam or anything but push it down very slightly 2 or 3mm and it fills with water. Is it because there's nothing to skim just yet? Takes about 20 mins to fill cup but doesn't overflow. Tia